STUDIES  OF  SULFUR  IN  RELATION  TO  THE 
SOIL  SOLUTION 


BY 

WILBUE  L.  POWERS 


CONTENTS 

PAGE 

Introduction 120 

Scope  of  the  experiments 124 

Relation  of  replaceable  bases  and  sulfofication  to  the  soil  solution 125 

Chemical  experiments 127 

Sulfur  and  sulfates  and  the  soil  solution 127 

Sulfur  and  soil  solutions  of  different  soils 130 

Sulfur  and  alfalfa  yield  with  soils  in  jars 133 

Hydrogen  ion  concentration  in  cropped  and  fallow  soil  pots 134 

Physiological  experiments 135 

Preliminary  studies 135 

Sulfur  and  chlorophyll 141 

Water  culture  experiments  with  seedlings 141 

How  does  sulfur  go  into  the  plants? 142 

Calcium  sulfate  versus  potassium  sulfate 143 

Complete  nutrient  solution  versus  displaced  soil  solution 146 

When  does  alfalfa  most  need  sulfur? 148 

Crop-producing  power  of  limited  amounts  of  sulfur  with  alfalfa 150 

Concentration  of  sulfate  needed  for  optimum  growth  of  alfalfa? 152 

Sulfate  concentration  experiments  with  culture  solutions 155 

Inorganic  sulfur 155 

Yield  and  inorganic  sulfate  content  as  affected  by  sulfate  concentration  ...  157 

Sulfate  concentration  experiment  with  solid  culture  medium 159 

Reaction  studies 160 

Discussion 161 

Is  sulfate  concentration  in  soil  solutions  sometimes  too  low  for  best  growth?  161 

Does  sulfur  serve  to  hold  calcium  and  other  bases  in  solution? 162 

Will  the  average  application  of  sulfur  hasten  soil  deterioration? 164 

Does  sulfur  improve  reaction  of  arid  soils  for  alfalfa? 164 

Summary 165 


120  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 


INTRODUCTION 

Sulfur  has  given  excellent  results  as  a  fertilizer  for  the  past  twelve 
years  when  applied  to  many  of  the  nearly  neutral,  semi-arid,  basaltic 
soils  of  the  northwestern  United  States,  especially  when  used  on 
legumes.  More  than  120,000  acres  in  Oregon  can  be  expected,  with 
sulfur,  to  yield  an  additional  ton  an  acre  of  alfalfa  a  year.  One-third 
of  this  area  has  been  sulfured. 

The  reason  for  the  marked  increase  in  yield  is  not  well  under- 
stood, even  though  an  extensive  literature  on  the  agrotechnic  use  of 
sulfur  has  accumulated.  Possible  deficiency  of  sulfur  in  soils  has 
not  been  seriously  considered  until  recently  when  better  methods  of 
analyses  revealed  much  larger  quantities  of  sulfur  in  plant  tissue  than 
was  reported  by  earlier  investigators.23  Assuming  that  the  quantity 
of  sulfur  in  plant  tissue  is  an  indication  of  the  amount  required  for 
normal  growth  processes,  it  is  readily  seen  why  sulfur  is  given  more 
consideration  than  formerly  in  studies  of  crop  production.  The  supply 
of  sulfur  found  in  soils  by  modern  methods  of  analysis51'  54  emphasizes 
the  relative  importance  of  this  element.  Elemental  sulfur  has  been 
extensively  studied  during  the  past  dozen  years  in  relation  to  its  effect 
on  soils,  soil  micro-organisms,  and  plants.  The  adequacy  of  the  supply 
of  sulphate  in  the  soil  solution  has  been  questioned  and  the  study  of 
gains  and  losses  in  soil  sulfur  has  been  given  much  attention. 

The  supply  of  sulfur  in  soils  is  in  many  instances  less  than  that 
of  phosphorous.50  The  total  sulfur  content  of  normal  soils  can  be 
expected  to  range  from  300  to  1200  pounds  in  two  million.40' 51  Many 
of  the  surface  soils  of  the  northwest  contain  less  than  500  pounds  of 
sulfur  in  2,000,000,  and  often  run  as  low  as  100  to  300  pounds  in  the 
plowed  surface  of  an  acre  in  leached  basaltic  land.  A  six-ton  alfalfa 
crop  may  remove  30  pounds  of  sulfur  an  acre.  Certain  soils  that 
have  been  cropped  for  a  generation  appear  to  have  lost  20  to  40  per 
cent  of  the  initial  sulfur  content.  The  sulfur  content  of  soils  seems 
to  vary  with  the  organic  matter  supply  and  is  usually  largest  in  the 
surface  soil. 

Analyses  of  percolate  from  lysimeters,  where  the  amount  drained 
out  annually  is  not  large,  may  indicate  the  nature  of  the  soil  solution.53 
The  percolate  from  the  Cornell  lysimeters  contains  sulfur  lost  at  the 
rate  of  30  to  4i  pounds  an  acre  each  year;40  in  Iowa,10  67  pounds; 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  121 

at  Rothamsted,46  71.6  pounds;  at  Bromberg,  Germany,19  about  100 
pounds;  and  in  Wisconsin23  and  at  Oregon  Experiment  Station  the 
loss  in  drainage  has  been  15  to  40  pounds  an  acre  a  year,  or  about 
four  times  the  amount  received  in  precipitation.50 

The  concentration  of  sulfate  ion  in  water  extracts  of  soil  has  often 
been  100  parts  per  million  or  more  and  often  approximates  half  the 
concentration  of  sulfate  in  the  displaced  soil  solution.  Burd9  reports 
concentrations  of  sulfate  in  displaced  solutions  from  California  soils 
of  from  118  to  655  parts  per  million.  Sulfate  was  found  to  increase 
in  fallow  and  to  help  hold  cations  in  solution,  especially  when  nitrates 
were  depleted  by  crops  or  reduced  by  anaerobic  bacteria. 

The  soil  solution  is  not  diluted  with  sulfur-free  rain  water.  Ames 
and  Boltz3  present  data  showing  9  pounds  of  sulfur  per  acre  in  the 
country  and  72  pounds  in  town  received  annually  from  rainfall. 
Different  investigators50  report  determinations  showing  wide  varia- 
tions between  amounts  of  sulfur  thus  gained  or  lost  in  different 
sections  of  the  country. 

Sulfur  is  often  added  to  land  in  barnyard  manure,  potassium 
sulfate,  ammonium  sulfate,  commercial  "superphosphate,"  or  as  cal- 
cium sulfate.  Especially  in  southeastern  United  States,  where  much 
commercial  fertilizer  is  used,  the  practice  tends  to  overcome  any 
possible  crop  depression  from  lack  of  a  sufficient  concentration  of  this 
nutrient  in  the  soil  solution.  Sulfur  seems  to  be  more  abundant  in 
soils  originating  from  granitic  rock  than  in  soils  of  basaltic  origin. 
Sulfates  may  accumulate  with  alkali,  as  in  the  Great  Basin  region, 
owing  to  absence  of  drainage  for  its  removal. 

Hart  and  Peterson  in  191123  announced  new  figures  for  the  sulfur 
content  of  crops,  showing  that  Leguminosae  and  Cruciferae  are 
especially  heavy  users  of  sulfur.  Reimer  and  Tartar51  found  that  a 
six-ton  crop  of  alfalfa  removed  about  30  pounds  of  sulfur  an  acre. 
Recent  data  by  Jones32  tends  to  reduce  this  amount  slightly. 

One  well  established  function  of  sulfur  is  that  of  increasing  the 
protein  content  of  alfalfa.51'  45  It  is  said  to  be  present  in  the  protein 
cystine.47'  53  Evidence  has  been  found  that  the  SH  group  in  cystine 
plays  a  catalytic  role  in  synthesis  of  vegetable  fats  in  plant  cells.44'  58 
Increased  root  and  nodule  development22'  51  and  a  richer  green  color 
have  commonly  resulted  from  use  of  sulfur  on  alfalfa.  Stiffer  straw 
and  heavier  seed  has  been  noted  from  sulfur  or  sulfate  applications 
to  grain  land15' 34  Harris  et  al24  reported  a  higher  concentration  of 
sulfate  in  the  leaf-tissue  fluids  of  Upland  than  of  Egyptian  cotton 


122  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 

and  suggest  that  this  difference  may  be  related  to  drought  resistance, 
alkali  resistance,  and  the  concentration  of  sulfate  ions  in  the  soil 
solution. 

Adequate  evidence  does  not  seem  to  have  been  found  to  establish 
any  close  relation  between  the  total  sulfur  in  soils  and  the  sulfate 
content  of  the  soil  solution  or  sulfate  requirement  of  crops.  It  seems 
probable  that  plants  may  contain  more  sulfur  than  required  perhaps 
both  in  organic  and  inorganic  form  where  the  sulfate  concentration 
of  the  soil  solution  with  which  they  are  grown  is  high. 

Numerous  investigators  have  found50  that  with  heavy  applications 
of  sulfur  to  soils  there  is  an  increase  in  concentration  of  free  hydrogen 
ions  somewhat  proportional  to  the  amount  of  sulfur  applied  and 
oxidized  to  sulfates.  Adams1  demonstrated  that  sulfate  formed  may 
be  leached  out,  while  the  acidity  is  not  removed.  Hydrogen  ion  seems 
to  participate  in  an  exchange  for  absorbed  cations,  such  as  calcium 
ion,  permitting  the  hydrogen  ion  to  remain  with  the  soil  as  an  acid 
silicate,  while  the  calcium  ion  is  leached  out  in  association  with  sulfate. 
The  amount  of  increase  in  concentration  of  hydrogen  ions  in  the  soil 
solution  as  a  result  of  sulfur  applications  may  depend  on  the  amount 
of  readily  soluble  bases  present  and  general  buffer  effects  of  the  soil. 

Lipman,30  Kelley,33  and  others  have  suggested  sulfur  for  correcting 
the  reaction  of  "black  alkali"  soil  by  increasing  the  hydrogen  ion 
concentration  upon  oxidation  and  combination  with  water.  This  acid 
may  then  dissolve  calcium  compounds  and  bring  about  exchange  of 
such  multivalent  bases  for  sodium  in  the  solid  phase  and  thus  improve 
permeability  and  reaction  of  "black  alkali"  land.  Johnson  and 
Powers30  found  sulfur  an  effective  chemical  treatment  for  such  land 
under  eastern  Oregon  conditions,  especially  when  used  in  combination 
with  gypsum  or  manure.  Sulfur  may  improve  the  reaction  of  an 
alkaline  soil,  flocculate  colloids  so  as  to  permit  better  drainage,  and 
tend  to  dissolve  calcium  from  its  compounds,  all  of  which  may  improve 
soil  conditions  for  legume  crops. 

The  Lipman37' 38  process  of  rendering  rock  phosphate  soluble 
depends  upon  the  production  of  acid  by  oxidation  of  sulfur  to  produce 
soluble  phosphate.  Lipman  and  his  associates  have  studied  the  most 
economical  proportion  of  soil,  sulfur,  and  "floats,"  best  suited  to 
moisture  and  climatic  conditions,  for  economical  production  of  avail- 
able phosphates.  Good  results  have  been  secured  in  western  Oregon 
by  applying  rock  phosphate  in  combination  with  sulfur  and  manure 
alternated  with  lime.50    A  reciprocal  relation  between  phosphates  and 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  123 

calcium  in  solution  in  the  soil  has  been  shown  by  Burd8  and  by 
Stephenson  and  Powers.50  A  moderate  increase  in  acidity  may  tend 
to  increase  phosphate  in  the  soil  solution  while  higher  acidity  may 
increase  calcium  ions  and  aluminum  ions  and  precipitate  phosphate 
to  a  relatively  insoluble  form. 

There  has  been  some  controversy  as  to  whether  calcium  sulfate  or 
sulfur  liberates  potassium  in  the  soil.  According  to  Lipman  and 
Gericke33  this  depends  upon  the  particular  soil.  Different  investi- 
gators have  reported  the  potassium  content  of  soil  water  extracts 
to  be  somewhat  increased  as  a  result  of  sulfur  or  sulfate  applica- 
tions.16' "- 46 

Maclntire39  has  pointed  out  a  relation  of  sulfur  applications  to 
increased  loss  of  calcium  in  percolate  from  lysimeters.  This  relation 
has  been  found  to  hold  true  with  two  Oregon  soils  employed  in 
lysimeters  at  Oregon  Experiment  Station.  Adams1  held  that  it  was 
difficult  to  find  much  calcium  in  solution  in  acid  soils  with  a  hydrogen 
ion  concentration  as  great  as  pll  5.0.  Stephenson  and  Powers56  found 
that  the  most  striking  effect  of  sulfur  on  water  extracts  of  three  soils 
tested  was  the  increase  in  calcium  ion  in  solution.  This  effect  would 
be  expected  to  be  less  marked  upon  acid  soils  which  have  been  rather 
thoroughly  leached  of  soluble  calcium  compounds. 

Nitrification  and  sulfofication  largely  result  from  biological  activi- 
ties. A  little  sulfur  may  stimulate  ammonifieation.49  Sulfur  may 
oxidize  and  unite  with  ammonia  as  sulfate  of  ammonia.2  McCool43 
finds  that  sulfur  aids  decomposition  of  organic  matter  and  formation 
of  nitrates.  A  little  sulfur  appears  to  aid  nodule  development49' S1 
and  nitrification45,  46  in  arid  soils,  while  larger  applications  may  result 
in  increasing  the  hydrogen  ion  concentration  sufficiently  to  depress 
nitrogen  fixation  and  nitrification.  Rudolfs54  observed  five  times 
more  bacteria  in  alkaline  soil  that  was  neutralized  by  sulfur.  Burd 
and  Martin11  have  noted  a  reciprocal  relation  between  the  amount  of 
nitrates  and  sulfates  obtained  in  the  soil  solution.  Whenever  sulfur 
stimulates  growth  of  legumes  an  increase  may  be  expected  in  nitrogen 
supply  in  the  soil  and  of  nitrate  in  the  soil  solution. 

Recent  investigations  lead  to  the  conclusion  that  the  supply  of 
available  sulfur,  like  the  supply  of  available  nitrogen,  follows  a  fairly 
definite  cycle.  Joffe29  concludes  that  making  acid  phosphate  by  the 
Lipman  process  is  chiefly  a  problem  of  providing  favorable  conditions 
for  sulfur  oxidation.  Brown  and  Kellogg7  find  that  soils  have  a  fairly 
definite  sulfur  oxidizing  power.6     Lipman  and  McLean38  report  that 


124  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

temperature,  aeration,  moisture  content,  and  proportion  of  materials 
affect  sulfur  oxidation,  and  they  find  no  advantage  in  starting  sulfur 
oxidation  with  a  soil  of  high  acidity.  Halversen  and  Bollen21  report 
that  sulfur  application  increases  the  sulfur  oxidizing  power  of  soils; 
they  find  little  need  for  inoculated  sulfur  for  many  Oregon  soils.  It 
appears  that  heavy  textured  soil  is  unfavorable  and  good  organic 
supply  is  favorable  to  rapid  sulfur  oxidation  in  soils.  Brown  and 
Gwinn5  note  that  phosphorus  and  manure  increase  sulfofication  in 
loam  soils.  Stephenson59  has  recently  demonstrated  that  the  rate  of 
sulfur  oxidation  is  related  to  the  surface  area  and  that  sulfur,  ground 
to  pass  a  forty-mesh  sieve,  should  oxidize  at  a  rate  adequate  to  meet 
plant  needs.  Boullanger  and  Dugardin4  suggest  that  certain  sulfur 
compounds  are  oxidation  catalysts.  The  possibility  that  sulfur  oxida- 
tion increases  anion  concentration,  thus  holding  cations  in  the  soil 
solution  and  bringing  about  conditions  favorable  to  base  exchange 
reactions,  will  be  developed  later. 

A  review  of  the  laterature  emphasizes  the  need  of  further  investi- 
gation as  to  the  role  of  sulfur  in  the  soil  solution. 

The  writer  wishes  to  acknowledge  his  indebtedness  to  Dr.  W.  F. 
Gericke  for  helpful  counsel  during  the  course  of  these  investigations. 


SCOPE  OF  THE  EXPERIMENTS 

The  primary  purpose  of  experiments  reported  herein  has  been 
to  determine  the  effects  of  sulfur  on  soil  solutions  and  their  relation 
to  sustained  crop  production.  The  study  has  included  the  effects  of 
sulfur  on  soil  reaction,  liberation  of  bases,  and  concentration  of  sulfate 
and  other  anions,  especially  as  related  to  the  nutritive  requirements 
of  alfalfa  at  different  growth  periods  and  to  sustained  productiveness 
of  soils. 

The  main  study  has  been  chemical,  supported  by  some  physio- 
logical experiments  and  confirming  field  trials,  and  has  included  four 
lines  of  attack,  as  follows :  ( 1 )  effect  of  sulfur  and  sulfates  on  the 
soil  solution;  (2)  effect  of  sulfur  on  the  solutions  of  different  soils; 
(3)  determination  of  the  minimum  optimum  concentration  of  sulfate 
for  alfalfa  by  the  water  culture  method;  (4)  confirmation  of  field-plat 
trials. 

The  soils  employed  and  some  of  their  characteristics  are  given  in 
table  1. 


1927] 


Powers:  Studies  of  Sulfur  in  Belaiion   to  the  Soil  Solution 


125 


EELATION  OF  BEPLACEABLE  BASES  AND   SULEOFICATION   TO   THE 

SOIL  SOLUTION 

The  soil  characteristics  presented  in  table  1  indicate  the  amount 
of  soil  solution  these  soils  can  retain,  their  total  sulfur  content,  sulfur 
oxidizing  power,  the  sulfate  content  of  their  displaced  soil  solutions, 
the  nature  and  amount  of  replaceable  bases  contained,  and  the 
response  of  these  soils  to  sulfur  treatment. 

TABLE  1 

Some  Characteristics  of  the  Soils  Used 


Soil  series  and  type 

Usable 
water 
capacity 
(approx- 
imate), 
acre-ins. 

per 
acre-ft. 

Total 

sulfur, 

lbs.  to 

2,000,000 

Sulfur 

oxidized 

in  14 

days, 

per  cent 

Sulfates 
displaced 

soil 

solution, 

p. p.m. 

Replace- 
able 

bases, 
per  cent 

of  soil 
Ca,  Mg, 

Na,  K 

Replace- 
able 
calcium 
per  cent 
of  soil 

Response 
to  sulfur 
in  field 

%" 

2" 

l'A" 

2V2" 

821 
240 

36 
17 
15 
18 

10 
4 
3 

140 

32 
464 

64 
168 

14* 

12« 
117t 

.0613 

.1734 
.7941 
.2322 
.1967 

4153 

.2876 

1  0816 

.0400 
.1248 
.6512 
.  1419 
.1383 

.3654 
.2600 
.8624 

Good 

2.   Umatilla  med.  sand  ... 

Slight 

4.  Yakima  sandy  loam 

5.  Deschutes  sandy  loam 

6.  Willamette  silty  clay 
loam  

403 

680 
280 
400 

Good 
Very  good 

Slight 

8.   Antelope  clay  adobe. 

Very  marked 

*  Growing  crop  May  7. 


t  2:1  extract. 


The  sulfofying  power  of  a  soil  seems  to  have  a  closer  relation  to 
the  sulfate  content  of  the  soil  than  does  the  total  sulfur  supply. 
Halversen  and  Bollen21  have  shown  the  relation  of  sulfur  oxidizing 
power  of  soils  to  sulfate  content.  As  sulfofication  is  largely  a  biological 
process,  providing  conditions  most  favorable  for  the  organisms  should 
aid  in  maintaining  a  favorable  sulfate  concentration  in  the  soil 
solution.  Application  of  manure  with  sulfur  has  appeared  to  be  an 
effective  aid  to  sulfofication  in  treated  alkali  land.30  Burd  has 
recently  reported  data8  emphasizing  the  importance  of  biological 
activities  in  keeping  up  a  favorable  concentration  of  nutrient  anions 
and  the  importance  of  supplying  sufficient  total  anion  concentration 
to  hold  favorable  amounts  of  cations  in  the  soil  solution.  Johnson31 
seems  to  show  that  growing  alfalfa  may  increase  the  sulfate-supplying 
power  of  a  soil.  This  may  be  due  to  plant  removal  of  sulfate  formed. 
The  forms  of  sulfur  in  a  soil  may  affect  rate  of  sulfofication. 

The  total  supply  of  replaceable  bases  and  the  proportion  of 
univalent  to  multivalent  bases  adsorbed  may  indicate  the  power  of 


126  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

recovery  of  a  soil  solution  after  exhausting  crops  and  the  properties 
likely  to  be  imparted  due  to  base  exchange  reactions.  Sulfur  may 
oxidize  and  then  unite  with  water  to  cause  an  increase  in  hydrogen 
ion  concentration  in  the  soil  solution.  The  presence  of  readily  soluble 
compounds,  such  as  calcium  carbonate,  under  such  a  condition  will 
favor  solution,  the  rate  of  which  will  depend  on  the  concentration  of 
acid  present.  Twentieth  normal  hydrochloric  acid  in  large  quantity 
has  been  found  to  be  capable  of  replacing  about  all  the  replaceable 
base  held  by  the  soil  adsorbing  complex  where  drainage  is  provided.17 
When  the  concentration  of  hydrogen  ion  or  other  cation  is  increased 
as  a  result  of  sulfur  oxidation,  base  exchange  may  occur.  This  is 
sufficient  to  indicate  the  close  and  important  relation  of  sulfur  oxida- 
tion, solubility  effects,  and  base  exchange  reactions  in  the  soil  system 
to  changes  in  its  liquid  phase.  Where  the  supply  of  replaceable  cal- 
cium in  table  1  is  low  and  response  from  sulfur  applications  marked, 
it  would  seem  to  indicate  that  sulfur  oxidation  results  in  solubility 
effects. 

Soils  2  and  6  (table  1)  give  little  response  to  sulfur  applications, 
and  these  soils  oxidize  sulfur  rapidly.  Soil  2  is  irrigated  with  water 
containing  two  or  three  pounds  of  sulfate  sulfur  per  acre-foot.  Soil  8 
oxidizes  sulfur  slowly  and  gives  marked  response  to  sulfur  appli- 
cations. 

In  order  to  learn  the  chemical  effects  of  sulfur  and  sulfates  on 
the  soil  solution  twenty-eight  two-gallon  stoneware  jars  that  had 
been  coated  with  valspar  were  filled  with  screened  surface  soil  of 
Madera  sand  type  which  was  known  to  give  typical  response  to  sulfur 
applications.  These  were  divided  into  groups  of  four  and  treated 
with  different  salts  (table  2)  at  a  rate  sufficient  to  supply  one  hundred 
pounds  of  sulfur  an  acre.  Three  jars  of  each  group  were  planted  to 
Grimm  alfalfa  while  the  fourth  was  fallowed.  Before  the  seedlings 
were  one  inch  high,  their  number  was  reduced  to  ten  uniform  sized 
plants  in  each  jar.  The  soil  was  maintained  at  about  optimum 
moisture  content  by  frequent  additions  of  distilled  water  and  the 
fallows  periodically  sampled  and  screened  and  their  solutions  dis- 
placed and  analyzed,  using  methods  described  by  Burd.11  Displace- 
ment of  the  soil  solution  is  accomplished  by  packing  the  soil  in  brass 
tubes,  adding  distilled  water  above  as  a  displacing  medium,  and  then 
air  pressure  from  the  top. 

Methods  of  analysis  employed  were,  for  the  most  part,  those  in 
use  in  the  plant  nutrition  laboratories  of  the  University  of  California 


1927]  Powers:  Studies  of  Sulfur  in  Belation  to  the  Soil  Solution  127 

and  recently  made  available  by  Hibbard.25  The  water  culture  tech- 
nique employed  has  been  described  by  Hoagland,28  Gericke,18  and 
Davis.14  Hydrogen  ion  concentration  determinations  of  solution 
cultures  were  colorimetric  and  of  displaced  soil  solutions  Avere  electro- 
metric.  Successive  portions  of  displaced  solutions  were  found  to  show 
fairly  uniform  electrical  conductivity  or  specific  resistance  until 
dilution  by  the  displacing  medium  began,  at  which  point  displacement 
was  terminated,  the  dilute  solution  discarded,  and  the  uniform 
solution  saved  and  analyzed. 


CHEMICAL  EXPERIMENTS 

SULFUR   AND   SULFATES   AND    THE    SOIL    SOLUTION 
Table  2 

The  treatments  given  to  portions  of  soil  are  indicated  in  column 
1,  table  2.  Sulfur  was  added  at  the  rate  of  one  hundred  pounds  per 
acre,  while  calcium  oxide  and  sulfates  were  added  in  quantities  con- 
tained in  gypsum  equivalent  to  one  hundred  pounds  sulfur  an  acre. 

The  composition  of  the  soil  solutions  displaced  from  treated  and 
untreated  fallow  jars  of  Madera  sand  as  determined  in  parts  per 
million,  after  6  weeks'  and  again  after  12  weeks'  incubation,  is  pre- 
sented in  table  2.  Analyses  are  also  given  for  the  solution  displaced 
from  the  original  soil  and  for  the  two  lots  receiving  heavy  sulfur 
applications  after  15  months. 

The  reaction  of  this  soil  on  the  untreated  field  plats  was  slightly 
alkaline  and  gave  a  pH  value  of  7.3.  Soil  from  sulfured  field  plats 
was  found  to  be  exactly  neutral.  After  6  weeks'  incubation  in  the 
green  house  a  very  slight  acidity  had  been  developed  in  untreated, 
fallow  jars,  as  shown  later  (table  6),  perhaps  owing  to  formation  of 
carbonic  acid  from  decomposition  of  organic  matter  under  the  moist, 
warm  conditions  in  the  greenhouse.  After  6  weeks'  time  the  develop- 
ment of  a  slightly  higher  concentration  of  hydrogen  ions  A\ras  observed 
in  soils  that  had  been  treated  with  sulfur  or  with  certain  sulfates. 
The  concentration  of  sulfate  ion  in  the  solutions  displaced  in  such 
cases  was  found  to  have  increased.  After  12  weeks'  incubation  the 
hydrogen  ion  concentration  had  increased  with  certain  sulfate  treat- 
ments, and  the  heavy  sulfur  application  resulted  in  hydrogen  ion 
concentrations  that  were  unfavorably  high  for  growth.  This  high 
acidity  .still  prevailed  after  15  months.    In  the  cropped  series  definite 


128 


University  of  California,  Publications  in  Agricultural  Sciences       [Vol.5 


acidity  developed  and  growth  appeared  to  maintain  a  hydrogen  ion 
concentration  of  about  pll  6.0.  Reaction  might  be  modified  by  decom- 
position of  organic  matter,  excretions  by  roots,  formation  of  sulfuric 
acid  in  sulfur  treated  pots,  as  by  hydrolysis,  and  selective  absorption 
of  cations,  added  in  certain  salts  such  as  sulfate  of  ammonia. 


TABLE  2 
Effect  of  Sulfur  and  Sulfate  on  the  Soil  Solution 
Analysis  reduced  to  10  per  cent  moisture   (wet  weight). 


Initial  soils 

Dec. 

Parts  per  million  soil  solution 

Treatment,  pounds  per  acre 

pH 

N03 

SOj 

PO, 

Ca 

K 

Mg 

7.3 

7.0 

47 
25 

140 
194 

4  5 
3  5 

119 
146 

57 
83 

129 

78 

Analysis  of  fallows   (after  six  weeks  incubation) 

X  untreated 

Sulfur,  100  lb. 

CaO 

SandCaO 

K2SO( 

CaSd 


X 

(NH,)2S04 

MgS04 

Displaced  soil. 

S-200 

S-500 


6  2 

116 

253 

4  0 

144 

98 

6  1 

161 

369 

3  5 

203 

125 

6.5 

127 

195 

6  0 

142 

88 

6.3 

156 

256 

5  0 

196 

105 

6  1 

157 

294 

3  0 

116 

172 

6  3 

120 

247 

3  5 

135 

112 

6  7 

70 

161 

4  0 

172 

60 

5  4 

150 

205 

4  0 

227 

63 

5  9 

53 

235 

4  5 

294 

63 

6  5 

.       30 

153 

4  0 

160 

27 

5.S 

38 

284 

5  0 

327 

125 

5  9 

21 

509 

3  5 

349 

133 

119 
221 

95 
156 
113 

90 

91 
121 
196 

98 
119 
102 


Second  analysis   (after  twelve  weeks) 


X 

s     

CaO 

CaO  and  S. 

K0SO4 

CaSO, 


X 

(NHO2SO4 

MgSO< 

Displaced  soil 
S-200 
S-500    ... 


6  1 

124 

261 

3  0 

207 

107 

6  3 

100 

341 

5  0 

382 

72 

6.7 

102 

204 

5  0 

324 

127 

6  7 

77 

322 

5  0 

356 

120 

6  5 

81 

282 

4  0 

361 

165 

6  6 

82 

224 

4  0 

351 

84 

5.8 

87 

190 

4  0 

139 

47 

5  6 

176 

258 

5  0 

326 

57 

5  6 

79 

241 

4  0 

268 

64 

6  4 

88 

219 

3  5 

124 

32 

4  8 

47 

376 

24  0 

376 

135 

4  4 

37     ' 

52  0 

156 

160 
131 
118 
144 
165 
79 

139 
128 
183 
14S 
157 
171 


Third  analysis   (after  fifteen  months) 


X 

S  200 

7.7 
3  8 
3  6 

44 

24 

1 

94 
672 
1510 

2  0 

1  0 

15  0 

79 
152 
171 

70 
174 
319 

S  500 

1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  129 

The  nitrate  in  field  plats,  treated  with  200  pounds  of  sulfur  per 
acre  about  a  year  previous  to  sampling,  was  lower  than  in  the  adjacent 
untreated  plat.  After  incubation  for  6  weeks  there  was  a  tendency 
toward  accumulation  of  nitrates  except  where  unfavorable  acidity  had 
developed.  After  12  weeks,  high  acidity  developed  in  heavily  sulfured 
jars,  which  made  conditions  unfavorable  for  nitrification  and  de- 
pressed the  supply  of  nitrate  to  or  below  that  of  the  untreated  soil. 
A  large  portion  of  the  nitrogen  in  the  ammonium  sulfate  applied 
appeared  later  as  nitrate. 

An  initial  supply  of  140  parts  per  million  of  sulfate  was  found  in 
the  soil  solution.  Since  this  soil  will  retain  about  10  per  cent  useable 
moisture  between  the  wilting  point  and  the  excess  point,  this  repre- 
sents 14  parts  per  million  sulfate  for  the  whole  system.  Sulfur  in 
the  field  trial  increased  the  sulfate  content  to  194  parts  per  million. 
Madera  sand  appeared  to  have  good  sulfofying  power,  even  with- 
out sulfur  additions.  Addition  of  sulfur  and  sulfate  substantially 
increased  the  sulfate  content  of  the  soil  solution  in  six  weeks.  Add- 
ing calcium  oxide  with  sulfur  appeared  to  retard,  rather  than  to 
encourage,  sulfofication.  Sulfofication  appeared  to  be  somewhat 
proportional  to  the  amount  of  sulfur  applied,  for  in  subsequent 
determinations  gains  in  sulfate  concentration  were  found.  Small 
differences  were  found  from  the  application  of  various  sulfates. 

The  amount  of  soluble  phosphate  first  seems  to  increase,  then  to 
decrease,  after  sulfur  treatment.  There  appears  to  be  a  little  depres- 
sion in  the  amount  of  phosphate  in  the  solution  after  sulfur  applied 
has  brought  considerable  calcium  into  solution.  With  heavy  sulfur 
applications,  marked  increase  in  acidity  and  increase  in  the  amount 
of  phosphate  were  found  in  the  soil  solution  after  12  weeks'  in- 
cubation. Increase  in  solubility  of  bases  such  as  calcium,  iron,  or 
aluminum  appears  to  have  resulted  in  precipitation  of  phosphate 
before  15  months  passed. 

Calcium  was  found  to  come  into  solution  strikingly  as  a  result  of 
sulfur  or  sulfate  applications.  Nearly  three  times  as  much  calcium 
was  found  in  the  soil  solution  following  heavy  applications  of  sulfur. 
Sulfur  appears  to  have  modified  the  soil  solution  with  respect  to 
calcium  more  than  with  any  other  ion. 

Potassium  was  brought  into  solution  in  the  soil  to  the  extent  that 
the  supply  in  solution  was  almost  doubled  by  heavy  applications  of 
sulfur.  Part  of  the  potassium,  when  applied  as  potassium  sulfate, 
appeared  to  be  fixed  by  exchange  reaction  with  other  bases  which 


130  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 

were  brought  into  solution.  Heavy  application  of  sulfur  resulted  in 
a  large  increase  in  potassium  ion  in  the  soil  solution  after  15  months. 
Either  potassium-bearing  compounds  were  slowly  dissolved  or  the 
calcium  had  participated  in  a  base  exchange  with  the  potassium  in 
the  solid  phase. 

Magnesium  ion  has  a  tendency  to  increase  in  concentration  in  the 
soil  solution  owing  to  sulfur  additions  and  possibly  also  to  base  ex- 
change reactions  following  an  increase  in  total  concentration  of  the 
soil  solution. 

The  analyses  in  general  indicate  that  a  very  important  function 
of  sulfate  is  that  of  bringing  in  and  holding  bases  in  solution.  It 
also  appears  to  increase  the  soil  acidity  with  a  resulting  increase  in 
availability  of  phosphate.  The  phosphate,  however,  may  tend  to  dis- 
appear if  the  soil  is  well  supplied  with  bases,  such  as  calcium,  which 
may  react  on  the  calcium  and  cause  precipitation  of  phosphate  from 
the  soil  solution.  This  reciprocal  relation  of  soluble  calcium  relative 
to  phosphate  has  been  noted  by  Burd.9 

SULFUR  AND   SOIL   SOLUTIONS    OF   DIFFERENT    SOILS 

Table  3 

Samples  of  typical  Oregon  soils  were  collected  from  old  sulfur 
experiment  fields,  including  soil  from  both  sulfured  and  unsulfured 
plats,  that  had  been  in  experiments  for  as  long  as  ten  years  and  had 
received  sulfur  generally  at  the  rate  of  one  hundred  pounds  per  acre 
every  three  or  four  years.  These  samples  were  screened  and  brought 
to  optimum  moisture  content,  allowed  to  stand  so  that  equilibrium 
would  be  established  between  the  solid  and  liquid  phases  of  the  system, 
and  the  displaced  soil  solutions  recovered  and  analyzed. 

Results  are  given  in  table  3  and  show  that  sulfur  applications 
increase  acidity  in  all  cases,  and  usually  more  than  0.5  pH.  There 
was  a  noticeable  difference  in  the  buffer  value  of  various  soils  used. 
The  Catherine  loam  did  not  resist  change  in  reaction  well  and  became 
unfavorably  acid.  The  nitrate  content  of  these  solutions  was  not 
greatly  modified,  but  gave  evidence  of  being  depressed  in  certain 
cases  from  sulfur  applications  on  acid  soils,  as  shown  in  the  case  of 
Catherine  loam. 

The  sulfate  content  of  Willamette  and  Carlton  soils  was  found  to 
be  very  low.  Samples  were  taken  from  these  soils  on  May  7  following 
a  cool  spring,  which  would  be  unfavorable  to  sulfur  oxidation,  and 
from  plats  supporting  winter  grain  that  had  attained  5  to  9  inches 


1927J 


Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution 


131 


height.  Both  these  humid  soils  are  subject  to  leaching  in  winter. 
Sulfofication  is  rapid  under  laboratory  conditions  in  the  Willamette 
soil  and  little  crop  increase  results  from  sulfur  applications  thereto, 
while  Carlton  soil  is  lower  in  total  sulfur  and  sulfate  and  responds 
to  sulfur  applications.  Sulfur  substantially  increased  the  sulfate 
content  of  all  soil  solutions.  There  was  a  tendency  for  sulfur  to 
increase  the  calcium  content  of  the  soil  solution,  and  also  the  potassium 
content. 

TABLE  3 

Effect  of  Sulfur  on  Soil  Solutions 

Soils  displaced  May,   1925,  reduced  to  comparative  moisture  basis. 


Soil 


Treatment 

pounds  per 

H2O 

pH 

N 

SO4 

po4 

Ca 

K 

acre 

200  S.  Ac. 

10% 

(wet 

24 

672 

152 

174 

basis) 

200  S.  Ac. 

10 

7  00 

25 

194 

3  5 

146 

83 

Untreated 

10 

7  30 

47 

140 

4  5 

119 

57 

3  x  100  S. 

15 

7.47 

51 

316 

1  0 

123 

96 

Untreated 

15 

7  84 

63 

153 

10  0 

100 

29 

3  x  100  S. 

10 

7  00 

54 

58 

3  0 

86 

31 

Untreated 

10 

7  76 

36 

37 

3  0 

86 

25 

100  S. 

15 

6  83 

20 

103 

2  0 

211 

86 

Untreated 

15 

7  67 

40 

75 

4  5 

164 

75 

2  x  100  S. 

20 

6  15 

18 

207 

2  0 

95 

75 

Untreated 

20 

6  83 

15 

13 

1  0 

41 

58 

3  x  320  S. 

20 

5  81 

trace 

46 

1  5 

42 

14 

Untreated 

20 

6  14 

none 

17 

4  0 

45 

11 

100  S. 

30 

5  47 

22 

555 

3  0 

328 

318 

Untreated 

30 
Fe 

6  57 

18 

114 

2.0 

142 

256 

Untreated 
3  x  200  S. 
3  x  400  S. 

.04 
08 
07 

117 
100 
74 

3  8 

3  0 

4  6 

100 
105 
152 

20  3 
17  3 
14  8 

Mg 


Madera  sand  field  sample 

1.  Madera  sand 

2.  Madera  sand 

3.  Deschutes  sandy  loam 

4.  Deschutes  sandy  loam 

5.  Umatilla  medium  sand 

6.  Umatilla  medium  sand 

7.  Yakima  sandy  loam 

8.  Yakima  sandy  loam 

9.  Carlton  silt  loam 

10.  Carlton  silt  loam 

Wheat  5"  May  7. 

11.  Willamette  silty  clay  loam 

12.  Willamette  silty  clay  loam 
Barley  9"  May  7. 

13.  Catherine  loam 

14.  Catherine  loam 

Water  extract,  two  to  one. 

15.  Antelope  clay  adobe 

16.  Antelope  clay  adobe 

17.  Antelope  clay  adobe 


78 

129 


Willamette  silty  clay  loam  and  Carlton  silt  loam  are  acid  soils, 
the  latter  occurring  in  the  low  foothills  of  the  Willamette  Valley.  The 
Willamette  soil  from  the  old  valley  filling  contains  a  fair  total  amount 
of  sulfur,  and  this  soil  has  a  high  sulf ofying  power  and  good  supply  of 
organic  matter.  It  gives  only  slight  response  to  sulfur  applications. 
Carlton  and  other  "redhill"  soils  are  low  in  total  sulfur  and  in  soluble 
sulfate  and  give  moderate  response  to  sulfur  treatment.  They  are 
also  low  in  soluble  calcium,  and  in  some  instances  the  soluble  potassium 
is  low.  Sulfur  may  help  to  bring  bases  into  solution  in  these  acid 
soils,  but  calcium  sulfate  may  be  more  safely  used. 


132  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 

Umatilla  medium  sand  receives  from  two  to  three  pounds  of  sulfur 
in  each  acre  foot  of  irrigation  water  and  requires  at  least  five  acre-feet 
of  water  a  season.  This  soil  is  rather  low  in  replaceable  bases  and 
does  not  afford  much  opportunity  for  base  exchange.  It  gives  slight 
response  to  sulfur  applications.  On  the  finer  soils  in  that  region  a 
moderate  increase  in  alfalfa  yield  is  secured  from  sulfur  applications. 

Catherine  loam  has  given  more  profitable  returns  from  calcium 
sulfate  than  from  sulfur.  The  reaction  of  this  soil  is  already  slightly 
acid  and  sulfur  may  develop  an  unfavorably  acid  condition.  This 
was  formerly  wild  meadow  land. 

Yakima  sandy  loam  and  Deschutes  sandy  loam  are  arid  soils  of 
nearly  neutral  reaction  with  large  total  supplies  of  calcium  and  having 
only  moderate  amounts  of  potassium  ion  in  their  soil  solutions.  The 
former  is  typical  of  the  main  soil  area  of  Klamath  Project.  Potassium 
salts  pay  when  applied  to  Deschutes  sandy  loam  in  which  potatoes  are 
growing,  and  sulfur  appears  to  bring  treble  the  amount  of  potassium 
into  the  soil  solution  in  this  soil.  The  alfalfa  crop  in  this  section  when 
soil-treated  with  sulfur  develops  an  especially  rich  green  color. 

The  samples  of  Antelope  clay  adobe  used  in  these  experiments 
come  from  the  sulfur  fertilized  plats  established  by  F.  C.  Reimer  north 
of  Medford  and  are  too  heavy  for  displacement,  so  water  extracts  were 
made.  The  amount  of  iron  in  solution  was  doubled  by  sulfur  applica- 
tions and  there  was  some  increase  in  calcium  ion  in  solution.  Iron 
pyrite  on  this  land  has  given  as  good  increase  in  alfalfa  yield  as 
sulfur,  after  time  was  allowed  for  oxidation  of  the  pyrite.  Ferrous 
sulfate  has  given  the  best  yields  in  plat  trials  at  this  experiment 
field.50 

After  the  analyses  above  given  were  completed,  ferric  chloride  was 
sprayed  on  two  plats  of  alfalfa  previously  unfertilized  and  a  vigorous 
growth  resulted,  showing  all  the  visible  results  commonly  secured 
from  sulfur  on  this  field.  There  is  a  possibility  of  iron  participating 
in  a  base  exchange  but  that  does  not  seem  to  have  been  an  important 
factor  here.  Iron  sulfate  has  been  successfully  used  to  overcome 
chlorosis  in  fruit  trees  where  applied  at  the  tree  roots  in  this  heavy 
soil. 

The  chief  effect  of  sulfur  may  depend  considerably  on  the  char- 
acteristics of  the  particular  soil  at  hand  and  its  reaction,  physical 
condition,  chemical  composition,  or  micro-organisms  present.  On  arid 
soils  of  slightly  alkaline  reaction  sulfur  may  improve  the  reaction  of 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  133 

the  soil  solution  for  alfalfa.  This  may  increase  the  solubility  of  iron 
in  the  soil  solution  and  favor  the  development  of  chlorophyll.  It  may 
also  favor  the  absorption  of  anions,  such  as  nitrates,  by  plants.  A 
better  supply  of  calcium,  as  -well  as  sulfate,  is  often  provided  by  an 
application  of  sulfur. 


SULFUR  AND  ALFALFA  YIELD  WITH   SOILS  IN  JARS 

Four  portions  of  each  of  these  soils  were  arranged  in  one-gallon 
jars,  two  being  treated  with  sulfur  at  the  rate  of  one  hundred  pounds 
an  acre,  the  others  untreated.  One  treated  and  one  untreated  jar 
containing  soil  of  each  type  were  then  planted  to  alfalfa  for  culture 
tests  and  for  displacement  and  analysis,  if  needed,  to  check  against 
field  plat  samples. 

The  increase  in  yield  of  alfalfa  secured  in  these  jars  as  a  result 
of  sulfur  treatment  ranged  from  7  per  cent  to  54  per  cent.  Umatilla 
sand  appeared  to  give  greate"  response  to  this  treatment,  in  the  jars 
and  irrigated  with  distilled  water,  than  under  field  conditions  Avhere 
large  amounts  of  irrigation  water  contributed  a  substantial  part  of 
sulfur  needed  by  the  alfalfa.  Ferric  chloride  was  found  to  be  about 
i  ■  effective  as  sulfur  on  Antelope  clay  adobe,  for  increasing  alfalfa 
yield  in  jars,  which  is  further  evidence  that  an  important  effect  of 
sulfur  on  this  soil  is  to  improve  availability  of  iron  and  overcome 
chlorosis  in  alfalfa  grown  in  it. 

A  preliminary  experiment  was  conducted  with  young  alfalfa 
transplanted  from  Madera  sand  soil  from  near  Delhi,  California. 
These  plants  had  grown  through  the  summer  season  on  soil  receiving 
no  sulfur.  Three  two-gallon  jars  were  untreated,  a  second  lot  of  three 
received  sulfur,  a  third  lot,  reprecipitated  calcium  carbonate  and 
sulfur,  a  fourth  received,  sulfur  as  calcium  sulfate,  and  the  fifth  lot 
received  potassium  sulfate  at  a  rate  that  would  supply  one  hundred 
pounds  of  sulfur  to  the  acre.  The  plants  were  set  out  December  29, 
1923.  Cuttings  were  made  when  the  growth  bloomed  freely,  February 
29,  May  5,  and  May  27.  One  jar  of  each  lot  was  not  harvested  at  the 
second  cutting  but  was  left  for  seed.  The  effect  of  sulfur  was  to  favor 
seed  formation.  Sulfur  or  sulfates  increased  the  height,  vigor,  and 
yield  of  alfalfa  in  this  trial  20  to  40  per  cent. 

Sulfur  reduced  the  water  requirement  about  one-third,  as  ex- 
pressed in  units  of  water  per  unit  of  dry  matter. 


134  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

Thirty-six  two-gallon  stoneware  pots,  paralleling  the  fallow  jars 
used  for  analyses,  were  planted  to  Grimm  alfalfa,  thinned  to  ten 
plants  per  jar  and  four  months'  growth  harvested  in  one  cutting  May 
27,  1924.  All  the  sulfates  were  applied  in  amounts  needed  to  provide 
one  hundred  pounds  per  acre  of  sulfur  and  gave  similar  increases  in 
yield.  The  jars  receiving  potassium  sulfate  attained  the  maximum 
height.  Moderate  increases  over  the  untreated  pots  were  secured  with 
calcium  and  with  sulfur  used  singly  or  combined.  The  increased 
efficiency  of  water  consumed  by  this  growth  in  treated  jars  was 
reflected  in  a  lower  water  requirement  per  unit  dry  matter.  A  more 
favorable  concentration  of  soil  nutrients  or  better  balance  in  the 
solution  should  lead  to  a  lower  transpiration  and  therefore  a  lower 
water  requirement,  unless  other  conditions  cause  small  yield  of  dry 
matter. 


HYDROGEN   ION   CONCENTRATION    IN   CROPPED    AND    FALLOW 

SOIL  POTS 

The  hydrogen  ion  determinations  were  made  about  every  two 
weeks  for  all  soil  in  jars.  Colorimetric  tests  were  made  promptly, 
after  sampling,  with  fresh  color  standards  checked  with  the  hydrogen 
electrode. 

Decomposition  of  organic  matter  on  untreated  fallow  pots  seems 
to  have  brought  the  reaction  down  from  pll  6.9  to  about  6.2.  Calcium 
carbonate  tended  to  maintain  a  more  nearly  neutral  reaction,  while 
heavy  application  of  sulfate  developed  an  unfavorably  acid  condition. 

Cropped  pots  when  untreated  developed  a  slight  acidity  and  main- 
tained a  pll  of  about  6.0.  There  was  a  somewhat  more  uniform 
reaction  in  cropped  pots  due  perhaps  to  the  tendency  of  plants  to 
maintain  a  favorable  reaction.  Results  strongly  indicate  that  a 
slightly  acid  reaction  is  brought  about  by  C02  evolved  by  growing 
roots  in  cropped  pots  or  from  decomposition  of  organic  matter  in 
fallows  forming  HCOa  as  suggested  by  Hoagland.JS  They  also  indi- 
cate that  a  slightly  acid  reaction  is  most  favorable  for  alfalfa  growth 
in  soil  and  that  moderate  applications  of  sulfur  may  improve  the 
reaction  of  basic  or  slightly  alkaline  arid  soils  for  alfalfa  nutrition. 


1927]  Potcers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  135 


PHYSIOLOGICAL  EXPERIMENTS 

In  order  to  test  the  adequacy,  for  alfalfa  growth,  of  sulfate 
concentrations  found  in  soil  solutions,  some  supplementary  water 
culture  experiments  were  undertaken.  It  was  hoped  that  this  would 
shed  further  light  on  the  sulfate  need  of  alfalfa,  the  form  in  which 
sulfate  is  best  obtained  from  the  soil  solution,  the  part  of  the  growth 
period  when  sulfate  is  most  needed,  the  crop-producing  power  of 
limited  amounts  of  sulfate,  and  especially  the  concentration  of  sulfate 
needed  for  best  growth.  For  this  work  fruit  jars  were  used  and  the 
seedlings  supported  on  flat  perforated  corks.  Molal  solutions  were 
prepared  of  di-potassium  acid  phosphate,  mono-potassium  acid  phos- 
phate, calcium  nitrate,  and  magnesium  sulfate.  Prom  these  stock 
solutions  a  culture  solution  was  made  up  to  an  osmotic  concentration 
equal  to  approximately  1  atmosphere  pressure  and  a  pll  value  of 
about  6.0.  Sulfur-free  culture  solutions  were  provided  by  substitut- 
ing calcium  nitrate  for  magnesium  sulfate,  and  limited  amounts  of 
sulfate  were  added  in  certain  experiments  from  a  saturated  solution 
of  calcium  sulfate  to  provide  the  number  of  parts  per  million  of  sul- 
fate desired.  A  fresh  solution  of  iron-tartrate  was  used  for  supplying 
soluble  iron.  In  these  experiments  records  were  kept  of  the  height 
and  vigor  of  plants,  the  amount  of  transpiration,  and  the  reaction  to 
culture  solutions.  The  reaction  tests  were  made  almost  daily  where 
there  was  a  tendency  to  deviate  from  the  optimum  range. 


Preliminary  Studies 
Tables  4  to  8 

Two-year-old  alfalfa  plants  were  secured  from  sulfured  and  un- 
sulfured  field  plats  near  Delhi,  where  crops  grown  on  Madera  sand 
had  shown  typical  response  to  sulfur.  The  crowns  of  plants  grown 
on  sulfured  fields  were  much  larger  than  those  of  the  same  age  from 
the  unsulfured  plats.  The  color  of  foliage  on  sulfured  land  was  a 
dark  green,  the  plants  presenting  a  marked  contrast  to  the  rather 
chlorotic,  unthrifty  plants  from  the  unsulfured  plats.  Sulfur  in  this 
field  trial  had  doubled  the  yield  of  alfalfa.     The  plants  Avere  washed 


136  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 

free  of  soil,  dried  on  a  blotter,  and  their  individual  weights  deter- 
mined. There  had  been  some  root  pruning  so  the  tops  were  clipped 
back  close  to  the  crowns.  The  plants  recovered  promptly  from  trans- 
planting when  placed  in  the  nutrient  solution. 

TABLE  4 

Alfalfa  Transplanted  from  Sulfur-Treatfd  Land 

Mean  yield  in  grams.     Dry  matter   (3  cuttings)   from  single  two-year-old  plants. 

Water 
Mean  yield  tops,  requirement 

Treatment  grams  tops 

A — Four-quart  jars.     Plants  from  sulfured  field. 

Complete  solution 8.4±  10  533 

Solution  lacking  S 4  5±  16  801 

B — Three-quart  jars.     Plants  from  unsulfured  field. 

Complete  solution .....  5  1±  24  589 

No  S.    Two  nitrates 1  9±  08  1377 

C — Two-quart  jars. 

Complete  solution  4.5±  24  612 

NoS.    Two  phosphates 2  1±  07  1285 

D.  I— Reaction  adjusted  April  1,  with  N/10  HsSOi. 

Complete  solution 2  4±  12  780 

NoS.    Two  nitrates 1  6±  05  1067 

NoS.    Two  phosphates 1  5±  02  1089 

D.  II— Reaction  adjusted  April  1,  with  N/10  HC1.  (Whole  plant.) 

Complete  solution .....  1  9±  06  598 

NoS.    Two  nitrates 1  4±  06  754 

NoS.     Two  phosphates 1  5±  08  751 

A  trial  was  made  with  twelve  plants  from  the  unsulfured  field 
plat,  the  plants  being  divided  evenly  into  two  lots  according  to  weight. 
Six  plants  were  placed  on  four-quart  jars  containing  complete  culture 
solutions  and  six  others  on  solutions  lacking  sulfur.  In  two  weeks  a 
difference  in  the  appearance  of  the  plants  was  noticeable.  The  plants 
provided  with  sulfate  developed  a  better  green  color  and  made  over 
twice  the  growth  during  the  first  two  months  compared  with  those 
grown  in  the  sulfur-free  solution.  The  plants  came  into  bloom  and 
were  cut  January  29,  April  23,  and  May  27,  1924.  The  yields  are 
presented  in  table  4,  section  A.  Approximately  twice  the  yield  of 
dry  matter  was  secured  from  plants  grown  on  solutions  provided  with 
sulfate.  These  plants  made  nearly  twice  as  efficient  use  of  water 
consumed  for  each  unit  of  dry  matter  produced  as  did  the  sulfur-free 
series. 

A  second  lot  of  plants  were  set  on  three-quart  jars  and  treated 
as  in  the  above  experiment,  except  that  the  sulfur-free  solution  in- 
cluded two  nitrate  salts  instead  of  two  phosphate  salts  as  in  the  above 


1927] 


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137 


138  University  of  California  Publications  in  Agricultural  Sciences        [Vol.5 

trial.  The  presence  of  two  nitrate  salts,  or  a  larger  supply  of  nitrates, 
was  associated  with  greater  yields  relative  to  untreated  plants  than 
was  secured  in  the  above  experiment  (table  4,  B) .  These  transplants 
were  one  year  old  and  sulfur  about  trebled  the  yield,  resulting  in  a 
transpiration  requirement  of  about  three-sevenths  of  that  from  the 
plants  grown  in  sulfate-free  solutions. 

A  third  lot  of  transplants  from  the  unsulfured  alfalfa  plats  were 
divided  into  lots  of  six  and  placed  on  two-quart  jars,  one-half  being 
provided  with  a  complete  culture  solution  and  the  others  with  a 
solution  lacking  sulfate.  The  yields  of  these  plats  are  presented  in 
section  C  of  table  4.  Where  sulfate  was  provided  the  plants  outgrew 
their  chlorotic  appearance  in  two  to  three  weeks'  time,  indicating  that 
lack  of  sulfate  was  the  cause  of  their  devitalized  condition.  The  total 
yield  for  plants  provided  with  sulfate  was  more  than  twice  that  from 
the  sulfur-free  series  for  three  cuttings,  and  consumed  less  than  half 
the  amount  of  water  per  unit  of  dry  matter  produced. 

A  fourth  lot  of  transplants  two  months  old  was  secured  without 
root  injury  and  set  on  three  dozen,  one-quart  culture  jars.  One  dozen 
of  these  jars  were  provided  with  a  complete  nutrient  solution;  a  second 
dozen  were  provided  with  a  water  culture  solution  lacking  sulfate 
and  containing  two  nitrate  salts;  and  the  third  dozen  were  provided 
with  nutrients  using  two  phosphate  salts.  When  these  plants  were  six 
weeks  old  they  developed  a  chlorotic  appearance,  and  at  that  time 
half  of  the  dozen  plants  in  the  sulfur-free  solution  were  brought  to  a 
favorable  reaction  by  the  use  of  N/10  sulfuric  acid.  To  six  other 
cultures  N/10  hydrochloric  was  applied  to  produce  a  favorable  re- 
action. Results  of  this  trial,  table  4,  section  I),  show  a  marked  increase 
in  yield  where  sulfate  was  included.  Applying  a  limited  quantity  of 
sulfate,  when  plants  had  been  grown  for  six  weeks  on  culture  solutions, 
produced  more  improvement  than  can  be  credited  to  improved  reaction 
alone.  In  all  these  trials  the  water  consumption  was  greatly  increased 
where  sulfur  was  lacking.  In  three  days'  time  the  sulfate  added  in 
acid  caused  a  dark  green  color  of  the  foliage,  which  was  noticeable 
until  the  plants  were  harvested  a  month  later.  This  difference  is  indi- 
cated in  figure  3. 


1927] 


Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution 


139 


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140  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 


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1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  141 


SULFUR  AND  CHLOROPHYLL 

Chlorophyll  determinations,  following  methods  described  by 
Willstatter,  with  the  whole  top  growth  from  sulfured  and  unsulfured 
alfalfa  in  soil  pot  trials,  yielded  12  per  cent  more  chlorophyll  where 
sulfur  was  applied.  Alfalfa  leaves  collected  from  sulfured  and  un- 
sulfured field  plats  showed  an  increase  of  18  per  cent  in  chlorophyll 
content.  The  effect  of  sulfur  in  increasing  width,  size,  and  color  of 
alfalfa  leaves  is  indicated  in  figure  2.  Lack  of  sulfur  resulted  in  a 
lack  of  rich  green  color  and  lack  of  vigor.  Data  in  table  3  show  that 
sulfur  application  increased  the  iron  content  of  the  water  extract 
from  Antelope  clay  adobe  and  this  iron  is  known  to  play  an  important 
role  in  chlorophyll  synthesis.  Sulfuric  acid  was  also  found  to  restore 
color  better  than  hydrochloric  acid  when  used  to  adjust  reaction  in 
culture  solutions. 


WATER   CULTURE   EXPERIMENTS    WITH    SEEDLINGS 
Table  5,  A 

To  check  the  plan  of  providing  sulfate  to  seedlings  in  partial 
culture  solutions  two  days  in  six,  three  series  of  cultures  were  pro- 
vided. In  the  first,  plants  were  exposed  to  calcium  sulfate  one  day 
in  five ;  in  the  second,  two  days  in  six ;  and  in  the  third,  four  days 
in  eight.  The  remainder  of  the  period  the  plants  grew  on  culture 
solutions  lacking  sulfur.  During  the  first  two  months  of  the  experi- 
ment the  best  growth  was  obtained  with  plants  exposed  to  calcium 
sulfate  two  days  in  six.  In  the  latter  part  of  the  growth  period  the 
plants  exposed  to  sulfate  only  one  day  in  five  forged  ahead  and  gave 
definitely  better  total  yields  both  of  total  and  marketable  dry  matter, 
indicating  that  extra  sulfur  was  most  helpful  in  the  early  part  of 
the  growth  period  and  perhaps  undesirable  later.  Figure  6  shows 
typical  plants  of  each  series  after  three  months'  growth.  There  was 
little  difference  in  the  yields  of  the  plants  exposed  two  days,  compared 
to  those  exposed  four  days  to  sulfate  solution,  as  shown  in  section  A 
of  table  5.  There  was  a  marked  difference  in  appearance  of  plants 
with  and  without  sulfur  in  this  and  other  trials,  as  shown  in  figure  7. 


142  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 

HOW  DOES  SULFUR  GO  INTO  THE  PLANT? 
Table  5,  B 

Sixteen  series  of  six  cultures  each  containing  three  Grimm  alfalfa 
seedlings  per  culture  were*  employed  in  an  experiment,  which  covered 
a  growing  period  of  110  days.  Plants  were  grown  on  culture  solutions 
lacking  sulfur  four  days  in  six  and  on  various  partial  culture  solutions 
containing  different  sulfates  two  days  in  six.    Solutions  were  changed 

TABLE  5 

How  Does  Sulfur  Go  Into  the  Plant? 

Alfalfa  yield  in  grams.     Dry  matter.     May  26,  1924. 

(Grown  on  sulfur-free  culture  solutions  and  transferred   to  solutions  containing 

sulfate  at  regular  intervals.) 

Mean  yield 

Whole  Water 

A.                                            Treatment                                                        culture  Tops  requirement 

3  plants  tops 

Complete  culture  solution,  unchanged           3.1  2.2±  08  855 

Complete  culture  solution,  changed  monthly                                        3  9  2  4±15  867 

S-free  solution,  unchanged                                                                         3  8  2  2±  16  851 

S-free  solution,  changed  monthly                                                             4  1  2  6±  10  712 

S-free  solution  4  days;  then  CaSOi  1  day                                                5  7  3  9±  23  569 

S-free  solution  4  days;  then  CaSC>4  2  days                                              4  2  2  7±  14  790 

S-free  solution  4  days;  then  CaS04  4  days                                              4  5  2  9±  23  651 

B. 

S-free  solution  4  days;  then  (NHOsSCU  2  days 3  6  2  7±  21  725 

S-free  solution  4  days;  then  MgSOi  2  days  18  1  2±  10  796 

S-free  solution  4  days;  then  K2SO4  2  days 5  3  3  6±  18  635 

S-free  solution  4  days;  then  Ca,  N03,  SO4  and  PO4  2  days 5  5  3  6±  13  639 

S-free  solution  4  days;  then  Mg,  NO3,  SO4  and  PO4  2  days  9  2  8±  69  1875 

S-free  solution  4  days;  then  K,  NO3,  SO4  and  PO4  2  days  4  6  3  3±  23  699 

S-free  solution  4  days;  then  Ca,  NChand  SOi  2  days 4  6  3  3±  06  691 

S-free  solution  4  days;  then  Mg.NOs  and  SO4  2  days  13  1  0±  16  1149 

S-free  solution  4  days;  then  K,  NO3  and  SO4  2  days  3  6  3  3±  21  638 

C.  Solutions  free  of  K  and  SO4  vs.  —  (Cation  supplied  only  2  days  in  6  and  with  SO4) 

S-free  solution  4  days;  then  CaSOj  2  days 

S-free  solution  4  days;  then  K2SO4  2  days 
S-free  solution  4  days;  then  (NH4>2S04  2  days  ... 

Complete  solution 

S-free  solution  4  days;  then  (NHMsSCU  (grain)  2  days 
Displaced  soil  solution  (6  weeks' growth) 
Displaced  soil  solution  plus  K2SO4 

frequently  during  the  latter  part  of  the  growth  period  to  avoid  con- 
tamination by  moving  the  plants  from  the  sulfur-free  nutrient  solution 
to  the  companion  solutions  containing  different  forms  of  sulfate.  The 
plant  roots  were  washed  by  standing  them  in  two-gallon  jars  of  tap 
water  for  twenty  or  thirty  minutes  and  then  rinsing  in  distilled  water 
before  transferring  from  one  partial  solution  to  the  other.  An  extra 
series  of  stationarv  controls  having  sulfur,  and  one  lacking  sulfur. 


4  3 

2  9±  11 

421 

2  9 

1  7±  10 

603 

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6666 

3  5 

2  5±  10 

603 

6  7 

5  5±  30 

539 

15 

l.li.ll 

750 

6 

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937 

1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  143 


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14-1  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

were  provided  to  test  the  effect  of  changing  the  nutrient  solutions 
monthly.  Changing  the  solution  showed  a  little  advantage,  as  did 
changing  the  plants.    This  was  probably  due  to  improved  aeration. 

Two  days  in  six,  series  8  to  12  received  sulfate  in  single  salt  solution 
as  calcium  sulfate,  potassium  sulfate,  ammonium  sulfate,  or  mag- 
nesium sulfate,  respectively.  During  the  first  two  months  of  this 
experiment  plants  receiving  sulfate  in  the  form  of  calcium  sulfate 
were  definitely  the  better  plants.  During  the  last  four  or  five  weeks 
of  the  experiment  these  were  overtaken  by  the  potassium  sulfate  series, 
the  yield  of  which  was  slightly  greater.  The  yield  with  ammonium 
sulfate  was  about  four-fifths  of  that  with  the  calcium  sulfate,  while 
the  magnesium  sulfate  scries  yielded  only  about  two-fifths  as  much 
as  the  calcium  sulfate  series. 

Series  12  to  14  were  provided  in  which  the  sulfate-bearing  solution 
received  nitrate,  phosphate,  and  sulfate  salts  of  the  base  under  con- 
sideration. Under  this  condition  calcium  salts  produced  one-eighth 
more  total  dry  matter  than  the  potassium  salts.  The  yield  with  mag- 
nesium sulfate  was  very  low. 

In  series  15  to  17  the  cations  were  supplied  in  both  nitrate  and 
sulfate  forms.  There  was  no  significant  difference  in  the  yield  ob- 
tained with  potassium  from  that  obtained  with  calcium  sulfate. 

In  all  trials,  solutions  containing  magnesium  salt  gave  very  poor 
results.  The  reaction  was  difficult  to  control  in  the  case  of  magnesium 
salt  solutions,  and  even  with  reaction  controlled  there  appeared  to 
be  magnesium  toxicity.  During  the  first  two  months  of  the  growth 
period,  calcium  sulfate  appeared  to  be  definitely  the  best  form  of 
sulfur  for  the  alfalfa  plants.  For  typical  plants,  the  relative  growth 
for  different  treatments  is  shown  photographically  in  figure  4. 

During  the  latter  part  of  the  growth  period  potassium  sulfate 
showed  advantage  in  certain  cases. 

CALCIUM  SULFATE  VEESUS  POTASSIUM  SULFATE 
Table  5,  C 
An  experiment  was  arranged  to  compare  further  the  value  of 
calcium  sulfate  with  that  of  potassium  sulfate.  In  this  experiment 
the  main  solution  was  deprived  of  both  sulfate  and  the  cation  con- 
cerned, so  that  it  could  be  obtained  only  during  the  two  days  out  of 
six  when  the  roots  were  in  the  partial  nutrient  solution  containing 
sulfate.  Thus  calcium,  potassium,  or  magnesium  was  held  out  of  the 
main  solution  and  applied  only  as  sulfates  in  the  partial  nutrient 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution 


145 


146  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

solutions  to  which  plants  were  transferred  two  days  in  six.  Also  nitro- 
gen, as  well  as  sulfur,  was  kept  out  of  a  certain  main  solution,  being 
provided  only  two  days  in  six  as  ammonium  sulfate.  In  this  experi- 
ment potassium  sulfate  gave  only  about  three-fifths  the  yield  of  tops 
and  of  total  dry  matter  as  was  secured  with  calcium  sulfate.  In  this 
trial  nitrogen  and  potassium  were  not  present  at  one  time,  and  the 
calcium  sulfate  excelled  during  nearly  all  of  the  growth  period,  as 
shown  in  figure  5.  During  the  period  when  the  plants  were  nine  to 
ten  weeks  old,  the  potassium  sulfate  series  and  calcium  sulfate  series 
were  nearly  equal  in  size. 

In  connection  with  the  value  of  potassium  sulfate  relative  to 
calcium  sulfate,  it  should  be  noted  that  calcium  encouraged  nmch 
branching  of  roots  and  a  bushy  top  growth,  or  cell  division ;  whereas 
potassium  produced  cell  elongation  and  seemed  more  important  at 
that  period  of  growth  when  the  alfalfa  was  making  its  maximum  in- 
crease in  height.  The  ash  of  alfalfa  contains  about  16.25  per  cent 
calcium  and  24.7  per  cent  potassium  and  the  oven  dry  alfalfa,  1.26  per 
cent  calcium  as  against  1.87  per  cent  for  potassium.32  As  shown  by 
Gericke18  potassium  is  best  supplied  to  plants  in  association  with 
nitrate,  and  this  was  verified  in  the  course  of  these  experiments. 


COMPLETE    NUTRIENT    SOLUTION    VERSUS    DISPLACED    SOIL 

SOLUTION 

Table  5,  C 

In  connection  with  these  experiments,  three  series  of  400  cc.  bottles 
were  provided,  set  with  two  alfalfa  seedlings  to  each  culture.  One 
set  was  filled  with  a  complete  nutrient  solution,  the  second  with  the 
natural  soil  solution  displaced  from  the  Delhi  soil,  and  the  third  series 
with  displaced  solution  reinforced  with  sulfate  applied  as  potassium 
sulfate.  After  the  first  few  weeks  the  displaced  solutions  made  little 
further  progress.  The  series  reinforced  with  sulfate  yielded  about 
three  times  as  much  dry  matter  as  the  natural  soil  solution,  but  only 
about  one-fifth  as  much  as  the  control.  At  Oregon  Experiment  Station 
sulfates  have  increased  growth  on  lysimeter  waters  even  where  the 
untreated  drainage  water  was  changed  frequently  and  where  the 
sulfate  concentration  in  the  percolate  was  similar  to  that  obtained 
from  displacing  the  same  soil  type.59 

A  similar  experiment,  to  be  reported  elsewhere,  dealt  with  the  best 
salt  for  supplying  calcium  ion  for  alfalfa  in  partial  solution  cultures. 


1927]  Poivers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution 


147 


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University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 


The  largest  yields  were  secured  with  calcium  supplied  as  sulfate.  A 
slightly  lower  yield  was  secured  with  calcium  nitrate,  and  much  less 
with  calcium  phosphate.  The  mean  weight  of  tops  from  six  weeks' 
growth  was  .96  gm.  with  calcium  sulfate ;  .80  gm.  with  calcium 
nitrate,  and  .20  gm.  with  calcium  phosphate. 


WHEN  DOES  ALFALFA  MOST  NEED  SULFUK? 
Table  6 

Six  series  of  cultures  were  arranged  to  determine  more  definitely 
the  time  in  the  growth  period  up  to  the  blooming  stage  when  alfalfa 
makes  the  maximum  demand  for  sulfur.  Three  series  were  started 
in  complete  solutions  while  three  companion  series  were  in  sulfur-free 
solutions.  After  three  weeks  the  first  pair  of  series  of  plants  was 
reversed  as  to  sulfur  supply.  The  second  pair  was  interchanged  after 
six  weeks,  the  third  pair  at  nine  weeks.  These  plants  were  harvested 
after  twelve  weeks '  growth.  The  advantage  of  having  sulfate  supplied 
during  the  first  six  weeks  of  this  growth  period  was  still  evident  at 
harvest  time,  as  shown  by  figure  7. 

In  all  three  cases  the  plants  started  in  the  sulfur-containing 
solution  gave  higher  yields.  There  was  some  indication  of  benefit  in 
the  case  of  plants  removed  from  sulfur  after  six  weeks,  and  there  was 
less  recovery  from  lack  of  sulfur  where  this  element  was  applied  late 
in  the  growth  period. 

TABLE  6 

At  What  Stage  in  Growth  Period  op  Alfalfa  is  Sulfur  Most  Needed? 
Twelve  weeks'  growth  period. 


Culture 

Treatment 

Mean  yield  in  grams 

Water 

series 

Whole  culture 

Tops 

requirement 
tops 

28 

3  9 
3.3 
3  6 

2  5 

3  8 
3.2 

2  4±  16 
2.3±  15 
2  4±  12 

1  8±07 

2  7±  23 
2  1±  12 

430 

28a 

519 

29 

449 

29a 

714 

30 

411 

30a 

608 

Solutions  used  in  this  trial  were  changed  each  month  and  analyzed. 
The  sulfate  content  for  solutions  containing  an  initial  concentration 
of  672  parts  per  million  of  sulfate  at  the  end  of  the  first  month's 
growth  showed  a  decrease  in  concentration  to  584  parts  per  million. 
The  solution  being  renewed,  it  was  decreased  in  concentration  to  450 
parts  per  million  the  second  month.     A  new  solution  was  reduced 


1927] 


Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution 


149 


150 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 


to  612  parts  per  million  the  third  month.  The  maximum  absorption 
of  sulfur  occurred  in  the  second  month  and  the  minimum  absorption 
in  the  third  month.  From  all  indications,  plants  seem  to  require 
sulfate  largely  during  the  earlier  part  of  the  growth  period,  pre- 
sumably in  building  up  their  system  after  the  seedlings  have  attained 
some  size.  Sulfur  applications  may  increase  the  sulfofying  power  of 
a  soil  and  residt  in  a  more  favorable  concentration  of  sulfate  ion  at 
critical  periods  of  growth.  In  all  these  experiments,  providing  a 
suitable  sulfate  supply  gave  a  lower  water  requirement. 


CKOP-PKODUCING  POWEE  OF  LIMITED  AMOUNTS  OF  SULFITE  WITH 

ALFALFA 

Table  7 

Eight  series  of  solution  cultures  were  prepared,  including  sulfur- 
free  controls  and  solutions  containing  5  to  30  parts  per  million  of 
sulfur  as  calcium  sulfate  arranged  in  increments  of  5  parts  per 
million.  One  part  per  million  is  equivalent  to  1  milligram  per  liter 
or  practically  the  volume  of  cultures  used.  Maximum  production  per 
milligram  sulfur  secured  was  .18  gms.  alfalfa  and  with  the  solution 

TABLE   7 

Crop  Producing  Power  of  Limited  Amounts  of  Sulfur 

Dry  matter  yield  in  grains,  six  weeks'  growth. 


Series 
No. 

Treatment,  approxi- 
mate (mgm's  S) 

Mean  yield 
whole  plant 

Yield  tops 

Water 
requirement 

Inorganic  S  as 
per  cent  SOj 

42 

No  S 

55 
.92 
1  02 
1   15 
1  06 
.97 
1  06 

43±  04 
.72±  03 
78±  01 
86±  05 
82±04 
82±  04 
.78±  02 

921 
486 
449 
412 
427 
460 
475 

101 

36 

.086 

37 

10  p. p.m.  S 

.127 

38 

.223 

39 

20  p. p.m.  S   ... 

.320 

40 

.238 

41 

30  p. p.m.  S 

.317 

containing  about  5  parts  per  million  sulfur.  Alfalfa  plants  were 
grown  thereon  and  when  a  month  old  showed  a  general  increase  in 
growth  up  to  the  series  containing  15  parts  per  million  of  sulfur. 
With  greater  sulfate  treatments  the  amount  of  growth  was  practically 
uniform.  When  the  plants  were  six  weeks  old,  10  parts  per  million 
of  sulfur  appeared  to  be  sufficient,  as  shown  by  figure  8.  The  plants 
had  attained  18  to  20  inches  in  height,  and  their  requirement  for 
sulfur  appeared  to  be  somewhat  diminished.  There  was  indication 
of  a  slight  stimulating  effect  with  10  parts  per  million  compared  to 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  151 


152  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

two  or  three  times  that  amount  at  the  later  growth  state,  as  shown  by 
figure  9.  It  was  necessary  to  harvest  before  the  plants  were  two 
months  old.  The  maximum  yield  was  secured  with  15  parts  per 
million  of  sulfur  in  the  solution.  That  there  was  no  significant  differ- 
ence between  this  and  the  control  or  the  series  receiving  larger  amounts 
of  sulfate  is  shown  graphically  by  figure  12.  The  sulfur-free  solution 
there  used  was  prepared  from  C.  P.  chemicals,  but  it  was  found  to 
yield  1.6  p. p.m.  sulfur  in  the  culture  solutions  as  used. 

Some  soil  solutions  from  Madera  sand  were  found  to  contain  150 
parts  per  million  of  sulfate.  Their  usable  water  capacity  was  less 
than  10  per  cent.  An  acre-foot  of  solution  would  not  be  stored  in 
less  than  10  acre-feet  of  such  soil,  giving  11  parts  of  sulfate  per  million 
in  the  total  mass.  In  the  soil,  diffusion  may  be  slower  than  in  the 
culture  solution. 

The  last  column  in  table  7  gives  the  sulfate  recovered  by  hot  water 
extraction  of  plants  grown  in  this  experiment.  A  much  larger  amount 
of  unassimilated  sulfate  appears  to  have  been  present  in  plants  grown 
on  solutions  containing  15  p. p.m.  or  more  of  sulfur. 

CONCENTEATION  OF  SULFATE  NEEDED  FOR  OPTIMUM 
GROWTH  OF  ALFALFA? 

Evidence  on  the  least  probable  concentration  needed  for  optimum 
growth  is  scarce.  The  concentration  of  different  ions  necessary  in 
solution  cultures  or  soil  solutions  is  not  definitely  known. 

Cameron12  matured  wheat  in  tap  water  which  was  claimed  to 
contain  0.5  parts  per  million  of  phosphorus  as  phosphate  ion. 

Burd10  suggested  that,  as  a  result  of  crop  removal,  the  concentra- 
tion in  a  soil  solution  may  fall  below  supplying  the  need  of  certain 
ions  by  plants.  He  reports  a  two-day  nitrate  supply  as  the  lowest 
concentration  found  under  growing  barley,  as  judged  by  the  rate  of 
crop  removal.  It  is  further  suggested  that  crop  removal  may  hasten 
solution  from  the  solid  phase  of  the  system. 

McCall  and  Richards42  found  a  higher  concentration  necessary  in 
quartz  cultures  to  give  equal  effect  with  water  cultures. 

Hoagland  and  Martin27  point  out  that  suitable  concentration  is 
affected  by  size  of  culture  vessel,  plants  to  be  grown,  rapidity  of 
growth,  reaction,  and  frequency  of  renewal  of  the  solution. 

In  an  experiment  previously  referred  to,  potassium  sulfate  greatly 
increased  the  yield  of  alfalfa  grown  on  displaced  soil  solution,  although 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  153 


2 


p 

5' 

3' 
to 


c 
p 
3 


154  University  of  California  Publication*  in  Agricultural  Sciences       [Vol.5 

there  was  already  an  apparent  abundance  of  potassium  present.  Cal- 
cium sulfate  or  potassium  nitrate  increased  the  yield  of  grain  grown 
in  lysimeter  water  in  recent  experiments  at  the  Oregon  Experiment 
Station,50  even  though  the  soil  water  was  frequently  renewed.  The 
study  of  crop-producing  power  of  limited  amounts  of  sulfate  indicated 
that  10  to  15  parts  per  million  of  sulfur  or  30  to  45  of  sulfate  might 
be  needed  for  best  growth  of  alfalfa.  Two  soil  solutions  studied 
contained  12  and  14  parts  per  million  respectively.  An  experiment 
was  planned  to  test  the  concentration  of  sulfate  needed  for  alfalfa  in 
culture  solutions,  and  also  in  a  solid  medium,  as  an  aid  in  interpre- 
tation of  soil  solution  analyses. 

SULFATE   CONCENTEATION  EXPERIMENT  WITH  CULTURE 
SOLUTIONS 

To  study  further  the  concentration  of  sulfate  needed  for  optimum 
growth  of  alfalfa,  a  new  experiment  was  planned  in  which  four  series 
of  alfalfa  plants  were  set  up  and  grown  in  each  concentration  of 
sulfate  employed,  so  that  one  series  from  each  lot  could  be  harvested 
at  intervals  of  10  days  and  subjected  to  chemical  tests.  Control  series 
were  arranged  without  sulfur  and  with  complete  nutrient  solutions. 
The  concentrations  of  sulfur  in  other  series  were  2,  4,  8,  16,  32,  and 
64  parts  per  million,  respectively.  Within  10  days  the  plants  without 
sulfur  were  making  poorer  growth  than  the  remaining  series.  The 
plants  had  been  set  on  the  jars  when  the  fourth  leaf  appeared  on  the 
seedlings.  Up  to  20  days'  growth  16  parts  per  million  of  the  element 
sulfur  in  sulfate  form  caused  a  more  rapid  growth  than  a  lesser  con- 
centration. Before  the  30-day  period  a  concentration  of  8  parts  per 
million  appeared  to  be  sufficient  and  this  condition  obtained,  so  far 
as  could  be  judged  by  height  and  appearance  of  plants,  to  the  close 
of  the  experiment.  The  amount  of  growth  for  different  concentrations 
is  indicated  in  figure  10. 

INORGANIC  SULFUR 

To  arrive  at  a  procedure  for  studying  the  unassimilated  or  in- 
organic sulfate  in  different  lots  of  these  plants  at  different  stages  of 
growth,  samples  of  alfalfa  grown  on  field  plats  at  Delhi  were  digested 
for  8  hours,  in  one  case  with  hot,  and  the  other  with  cold  water.  The 
pulp  was  filtered  out,  washed,  and  the  extract  acidified,  redigested, 
and  filtered  free  from  protein.  The  sulfate  was  then  precipitated 
with  barium  chloride,  ignited,  and  weighed.     Further  tests  were  made 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution 


155 


3 
o5' 


%9 

=  3 


LA  <f' 


156  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

by  an  additional  1  hours'  digestion  of  the  pulp,  which  indicated  that 
digestion  with  hot  water  for  a  period  of  12  hours  was  desirable. 

A  second  preliminary  experiment  was  conducted  on  1  gram  por- 
tions of  alfalfa  meal  diluted  with  water  up  to  10,  25,  50,  and  100  times. 
Little  advantage  was  found  in  diluting  above  25  times  and  none  above 
50  times.  Grimm  alfalfa  seed  carried  through  this  determination 
yielded  0.3  per  cent  of  sulfate. 

The  alfalfa  grown  in  water  cultures  with  limited  amounts  of 
sulfate  when  analyzed  by  this  method  showed  a  rapid  increase  in 
sulfate  content  up  to  15  parts  per  million,  a  further  gradual  increase 
up  to  30  parts  per  million,  and  little  or  no  increase  thereafter  (table 
7 ) .  In  other  words,  the  supply  of  inorganic  sulf ates  in  these  young 
plants  increased  with  the  growth  curve.  Peterson48  and  Hall20  seem 
to  find  only  a  small  portion  of  sulfur  in  alfalfa  plants  in  inorganic 
form.  Determinations  of  organic  sulfur  from  the  residue  of  30- 
day-old  plants  were  made  and  indicate  a  reciprocal  relation  to  the 
inorganic  sulfur  content. 


YIELD   AND   INORGANIC   SULFATE    CONTENT    AS   AFFECTED    BY 
SULFATE  CONCENTRATION? 

Table  8 

In  table  8  are  presented  the  yield  and  the  hot  water  extractable 
sulfate  from  alfalfa  plants  grown  in  solutions  with  definite  concen- 
trations of  sulfate,  maintained  by  renewing  the  solution  every  three 
days.  The  yield  of  dry  matter  in  plant  tops  was  increased  by  supply- 
ing sulfur  up  to  8  to  16  parts  per  million  as  sulfate  in  the  solution. 
During  the  earliest  part  of  the  experiment  16  parts  per  million  of 
sulfur  seemed  to  give  better  growth  than  8  parts  per  million.  Later 
in  the  experiment  the  lower  concentration  appeared  to  be  fairly 
adequate.  Sulfate  determinations  indicated  that  some  ex-osmosis  of 
sulfate  occurred  for  higher  concentrations  the  last  10  days  of  the 
trial.  With  these  plants  there  was  further  evidence  of  some  stimula- 
tion about  the  least  optimum  concentration,  as  shown  graphically  in 
figure  13. 

The  sulfate  extractable  in  hot  water  increased  rapidly  up  to  the 
least  concentration  necessary  for  optimum  growth.  A  greater  supply 
of  inorganic,  or  hot  water  extractable  sulfate,  was  found  in  the  plants 
at  30  days  of  age  than  at  earlier  or  later  growth  periods.  It  appears 
that  as  fast  as  the  plants  gain  some  capacity  a  considerable  amount 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Soluti 


157 


158  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  5 


/*/,///$  ram  i    o  f \St*/f>  n  *r 

Fig.  12.     Graph  showing  yield  from  limited  amounts  of  sulfur. 


E  FFECT  OF  SULPHATE  CONCENTAT/ON ON THE  YIELD  OF  ALFALFA 

FOX  30  DA  Y  PER  tOP 

Fm  /3 


.2  O 


'S 


?__/.<? 


Concentration  ofSO^  ,  parts  per  m////ori. 


Fig.  13.  Grapli  showing  yield  from  culture  solutions  maintained  with  different 
concentrations  of  sulfur. 


1927] 


Powers:  Studies  of  Sulfur  in  B  elation  to  the  Soil  Solution 


159 


of  sulfate  is  taken  in,  and  later  this  sulfate  is  assimilated.  Plants 
grown  in  the  plant  house  at  the  University  of  California  were 
benefited  rather  than  injured  by  removing  them  from  a  complete 
solution  after  the  first  six  weeks  to  a  solution  lacking  sulfate,  and  they 
appeared  to  have  sufficient  sulfate  to  carry  them  up  to  the  blooming 
period. 

TABLE  8 

Effect  of  Sulfate  Concentration  of  Culture  Solution  on  Yield  and  Sulfate 
Content  of  Alfalfa  at  Different  Stages  of  Growth 


Sulfur  p. p.m.  in 

Mean  yield  in  grams  dry  plant  tops 

Plant  sulfate  extractable  with 
hot  water,  per  cent 

culture  solution 
(added  as  CaSCW 

Growth  period — days 

Age  of  plants— 

days 

10 

20 

30 

40 

10  and  20 

30 

40 

None 

01 ±001 

02±  002 

.  05±  006 

09±002 

000 

.150 

.074 

2 

Oli.OOl 

03±  002 

07±  003 

23±  006 

.068 

652 

291 

4 

02±  001 

04±  002 

23±  005 

.63± 

.217 

750 

.285 

8 

02±  000 

09±  005 

37±  007 

79±  016 

440 

.886 

255 

16 

02±  000 

07±  003 

28±  005 

85±027 

506 

1  165 

.259 

32 

02±  001 

09±004 

28±007 

79±018 

.386 

896 

350 

64 

02±001 

10±  005 

27±  Oil 

76±  021 

.929 

.975 

.448 

Complete  solution 

02±  004 

04±  002 

14±  003 

43±  012 

.979 

1  410 

317 

From  these  studies  it  appears  that  8  to  16  parts  per  million  of 
sulfur  or  24  to  48  parts  per  million  expressed  as  sulfate,  depending 
on  age,  is  sufficient  for  best  growth  of  alfalfa  for  these  conditions. 
The  sulfate  contents  of  displaced  soil  solutions  from  a  half-dozen 
representative  Oregon  soils  (that  have  been  included  in  sulfur  experi- 
ments seven  to  ten  years  both  with  and  without  sulfur)  reported 
above,  throw  further  light  on  this  problem. 


SULFATE    CONCENTRATION    EXPERIMENT    WITH    SOLID    CULTURE 

MEDIUM 

A  parallel  experiment  was  conducted  in  pots  of  quartz  sand  to 
note  the  effect  of  a  solid  medium  on  concentration  and  diffusion. 
Duplicate  one-gallon  jars  of  washed  Ottawa  silica  sand  were  arranged 
so  that,  with  the  aid  of  an  aspirator,  solutions  could  be  removed  for 
renewal.  Five  alfalfa  plants  were  grown  in  each  jar.  The  yield  was 
not  increased  with  solutions  containing  more  than  8  parts  per  million 
of  sulfur.  It  is  possible  that  transpiration  changed  the  concentration 
of  sulfate  during  the  3-day  intervals  between  solution  changes, 
although  a  little  free  liquid  was  present  in  the  bottom  of  each  jar. 


160  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

There  may  have  been  a  concentration  of  sulfate  at  the  surfaces  of  the 
quartz  grains. 

The  rate  of  diffusion  of  sulfate  ion  may  be  expected  to  vary  with 
a  number  of  factors  and  a  study  is  under  way  in  quartz  flour  and 
quartz  sand. 

Two  lots  of  quartz  flour  and  two  of  quartz  sand  moistened  to  the 
moisture  equivalent  point  were  placed  in  trays  25  x  25  x  60  cm.  The 
two  sides,  one  moistened  with  .01  N  KC1,  the  other  with  .01  N  H2S04, 
were  brought  into  contact  and  kept  air  tight  at  uniform  temperature. 
In  45  days  quantitative  determinations  of  1 :1  extracts  showed  that 
sulfate  had  diffused  4  to  6  cm.  in  the  quartz  flour  and  8-10  cm.  in  the 
sand.  After  90  days  a  second  test  showed  that  diffusion  had  pro- 
ceeded at  a  uniform  rate.  Apparently  roots  go  to  the  nutrient  more 
than  nutrient  goes  to  the  roots.  Concentration  due  to  transpiration 
and  surfaces  may  tend  to  compensate  for  slower  diffusion  in  solid 
medium  than  in  solution  cultures.  Results  indicate  that  a  suitable 
sulfate  concentration  in  medium  sand  is  not  greatly  different  from 
that  needed  in  water  cultures. 


KEACTION  STUDIES 

The  reaction  of  the  solutions  used  in  the  water  culture  studies 
above  described  was  corrected  almost  daily  where  necessary,  to  keep 
it  between  pH  5.5  and  6.0,  which  appears  to  be  most  favorable  for 
alfalfa  in  solution  cultures.  At  or  above  pH  6.5  a  lighter  green  color 
developed  in  tops  and  a  brown  color  on  roots.  Below  pH  4.8  roots 
became  dull  in  appearance  and  growth  was  retarded. 

One  culture  series,  table  5,  c,  was  set  with  barley  seedlings  to 
compare  the  rate  of  change  in  reaction  in  a  single  salt  solution  of 
ammonium  sulfate  with  grain  to  that  induced  by  alfalfa.  The  reaction 
became  unfavorably  acid  with  grain  in  about  half  the  time  required 
with  alfalfa.  Alfalfa  removes  sulfate  from  solution  at  about  the 
same  rate  as  ammonium  ion  and  affords  less  opportunity  for  the 
sulfate  radicle  to  accumulate  in  the  solution  and,  by  combination  with 
water,  to  increase  the  concentration  of  hydrogen-ions. 

To  learn  more  definitely  the  reaction  best  suited  to  inoculated 
alfalfa,  water  culture  solutions  were  prepared  containing  only  20 
parts  per  million  nitrogen  and  with   different  pH   values.*      Eight 


*  This  experiment  was  conducted  in  cooperation  with  Mr.  Charles  Hartmann, 
Jr.,  former  Assistant  in  Soils,  Oregon  Agricultural  Experiment   Station. 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  1(51 

stoneware  jars,  each  of  4-gallon  capacity,  were  provided  with  covers 
so  as  to  support  25  plants  per  jar  and  Avere  filled  with  nutrient 
solutions.  Two  jars  were  filled  with  "complete"  nutrient  solutions 
and  adjusted  to  a  pH  value  of  5.8.  The  other  solutions  were  of  similar 
salt  proportions  except  that  little  nitrate  was  present.  The  reaction 
was  stabilized  by  addition  of  potassium  acid  thalate  in  all  cases 
equivalent  to  200  parts  per  million.  Two  jars  were  made  up  to 
pH  5.2,  a  second  pair  to  pH  6.0,  and  a  third  pair  to  pH  7.2.  A  fair 
growth  was  obtained  in  all  but  the  alkaline  solutions.  The  average 
yield  for  controls  for  2  months'  growth  was  .35  gram  tops  per  plant. 
Cultures  maintained  at  pH  7.2  yielded  .13  gram  of  tops,  and  those 
kept  at  pH  5.2  yielded  .21  gram  tops  per  plant. 

The  greatest  development  of  nodules  occurred  on  roots  of  plants 
grown  at  pll  6.0.  Nodules  developed  in  the  control  the  last  week  of 
the  experiment.  The  range  of  pH  in  which  alfalfa  can  grow  appears 
to  be  about  pH  4.8  to  7.0  and  to  be  wider  than  for  alfalfa  bacteria, 
which  will  not  tolerate  such  an  acid  solution  as  will  alfalfa.  Alfalfa 
appears  to  do  best  in  a  slightly  acid  culture  medium.  The  equipment 
used  and  the  comparative  growth  in  different  solutions  after  5  weeks 
is  shown  in  figure  11. 


DISCUSSION 

Is  Sulfate  Concentration  in  Soil  Solutions  Sometimes 
Too  Low  for  Best  Growth? 

A  study  of  gains  and  losses  of  soil  sulfur,  its  oxidation,  and  the 
seasonal  sulfate  concentration  in  the  soil  solution,  strongly  indicates 
that  certain  soils  at  times  have  an  unfavorably  low  supply  of  this 
nutrient.  Sulfate  concentration  in  the  soil  solution  is  apparently 
more  closely  related  to  the  sulfofying  power  of  a  soil  than  to  its  total 
sulfur  content.  Many  northwestern  soils,  however,  with  only  150  to 
400  pounds  total  sulfur  in  the  plowed  surface  of  an  acre,  respond  to 
sulfur  applications,  while  relatively  few  having  more  than  500  or 
600  pounds  of  sulfur  in  2,000,000  of  surface  soil  give  much  response 
in  the  way  of  increased  yield  from  sulfur  applications.  In  the 
1916  series  of  Reimer  plats  on  Antelope  clay  adobe,  near  Medford, 
any  sulfur-bearing  fertilizer  has  strikingly  increased  alfalfa  yields. 
Sulfur-free  fertilizers  supplying  soluble  phosphates,  potassium,  or 
nitrates  have  not  materially  increased  yields.    Moreover,  calcium  com- 


162  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

pounds  in  these  trials  have  not  caused  larger  crops.50  These  facts 
led  to  the  view  that  many  basaltic  soils  in  the  northwest  were  in  need 
of  sulfur  per  se.  Studies  herein  reported  have  developed  good  evi- 
dence that  unfavorably  low  concentrations  of  sulfate  are  less  general 
than  formerly  supposed,  yet  they  may  be  found  at  times  in  certain 
soils. 

Reviewing  the  evidence  here  presented,  it  is  noted  that  certain 
soil  solutions  were  found  which  in  certain  cases  yielded  but  14  and 
16  parts  per  million  of  sulfate.  For  a  given  set  of  conditions,  the 
crop-producing  efficiency  of  a  limited  amount  of  sulfur  decreases 
below  a  certain  minimum.  Sulfur  in  alfalfa  seed  seems  to  be  insuf- 
ficient to  develop  properly  and  to  mature  alfalfa  plants.  Further, 
the  least  optimum  concentration  of  sulfate  for  alfalfa  appears  to 
range  from  48  to  '24  parts  per  million  during  the  early  weeks  of  the 
growth  period.  The  maximum  demand  and  perhaps  the  whole  need 
of  sulfate,  moreover,  is  met  during  these  early  weeks  of  the  growth 
cycle,  when  sulfur  oxidation  on  certain  soils  has  been  slow  and  sulfates 
in  the  soil  may  have  been  depleted  by  leaching  in  the  wet  season. 
Diffusion  in  medium-textured  soils  may  be  much  slower  than  in  water 
culture  solutions.  Numerous  factors  will  affect  the  concentration 
needed,  as  pointed  out  by  Hoagland  and  Martin.-'7  Johnson's  work31 
seemed  to  indicate  that  reaction  may  affect  sulfate  absorption  by  plants 
from  solution  of  low  sulfate  concentration ;  also,  that  acid  or  humid 
soil  may  supply  sulfate  needed  from  a  lower  concentration  than  that 
in  neutral  soils,  and  that  sulfate  production  in  soil  is  increased  by 
cropping.  Diffusion  will  vary  with  temperature,  surface  tension, 
texture,  and  moisture  content.  Sulfate  additions  to  certain  soil  solu- 
tions and  lysimeter  waters"'''  used  as  culture  media  for  alfalfa  and 
grain  seedlings  have  increased  the  growth  of  these  plants. 

The  majority  of  soils  studied  which  respond  to  sulfur  applications 
with  alfalfa  have  100  parts  per  million  or  more  of  sulfate,  and  other 
reasons  for  the  marked  increases  in  yields  secured  from  this  treatment 
must  be  found. 

Does  Sulfur  Serve  to  Hold  Calcium  and  Other  Bases  in   Solution? 

It  has  been  noted  in  lysimeter  studies  at  different  experiment 
stations  that  there  is  a  mutual  effect  of  calcium  and  of  sulfate  on  the 
composition  of  the  percolate.  Supplying  either  of  these  ions  tends 
to  increase  the  amount  of  the  other  found  in  a  given  amount  of 
percolate  from  lysimeters.59 


1927]  Powers:  Studies  of  Sulfur  in  Relation  to  the  Soil  Solution  163 

The  most  striking  and  general  effect  of  sulfur  on  the  soil  solution 
encountered  in  these  experiments  is  the  increase  in  concentration  of 
calcium,  following  application  of  sulfur  or  sulfate.  This  has  been 
true  not  only  for  fallowed  pot  experiments  but  for  samples  from 
sulfured  and  unsulfured  field  soils.  In  certain  cases,  as  with 
Deschutes  sandy  loam,  potassium  concentration  in  the  soil  solution 
was  greatly  increased  following  sulfur  treatment.  Increase  in  mag- 
nesium in  the  soil  solution  is  also  noticeable  following  sulfur  applica- 
tion. The  calcium  in  solution  is  frequently  doubled  or  trebled  as  a 
result  of  sulfur  application. 

Water  culture  experiments  show  that  where  sulfates  of  calcium, 
potassium,  or  magnesium  are  supplied  to  alfalfa  plants  in  partial 
nutrient  solutions,  2  days  in  6,  calcium  sulfate  is  the  most  favorable 
form  and  results  in  the  largest  amount  of  growth.  Inversely,  when 
calcium  is  supplied  in  partial  solutions  as  sulfate,  nitrate,  or  phos- 
phate, the  calcium  sulfate  is  a  very  favorable  source  of  calcium. 

The  amount  of  readily  soluble  and  of  replaceable  calcium  and  other 
bases  present  in  a  soil,  as  indicated  by  Kelley,33  is  closely  related  to 
the  composition  of  the  soil  solution.  Madera  sand,  after  6  or  12  weeks 
of  incubation  with  sulfur,  was  found  to  have  released  large  amounts 
of  calcium  to  the  liquid  phase.  The  replaceable  calcium  in  this  soil 
is  low  and  some  carbonates  probably  were  dissolved.  A  year  later 
the  amoxint  of  calcium  in  solution  had  greatly  decreased  and  the 
potassium  in  solution  had  markedly  increased.  Either  there  had  been 
a  slow  solubility  effect  on  relatively  insoluble  potassium-bearing  com- 
pounds in  the  solid  phase,  or,  what  is  more  probable,  the  calcium  ion 
brought  into  solution  from  carbonates  had  participated  in  a  base 
exchange  with  the  base-absorbing  complex  of  the  soil. 

An  important  function  of  sulfur  or  other  anions,  as  pointed  out 
recently  by  Burd,8  appears  to  be  that  of  holding  cations  in  solution 
and  thus  maintaining  a  favorable  concentration  of  nutrients  in  the 
soil  solution.  He  has  suggested  that  when  nitrate  is  largely  removed 
by  growing  crops  the  sulfate  operates  to  perform  this  function  and 
to  keep  bases  in  available  form.  A  4-ton  crop  of  alfalfa  requires  about 
300  pounds  of  calcium.32  The  concentration  of  calcium  ion  in  the 
soil  solution  for  some  of  the  soil  types  studied  has  been  found  to  be 
as  low  as  20  or  30  parts  per  million  at  certain  times.  At  present  it 
appears  that  one  of  the  leading  effects  of  sulfur  is  to  bring  calcium 
and  other  bases  into  the  soil  solution  and  to  hold  them  there. 


1(U  University  of  California  Publications  in  Agricultural  Sciences       [Vol.5 

Will  the  Average  Application  of  Sulfur  Hasten  Soil  Deterioration? 

Recent  studies  by  Gedroiz17  and  others  indicate  that  the  replace- 
able bases  adsorbed  by  the  soil-adsorbing  complex  of  a  fertile  soil 
should  be  mainly  calcium  or  the  bivalent  bases,  calcium  and  mag- 
nesium. Further,  that  when  this  adsorbing  complex  becomes  unsatur- 
ated with  bases,  as  in  aged  acid  soils,  and  contains  much  adsorbed 
hydrogen  ion  instead,  these  complex  silicates  may  tend  to  become 
unstable  and  to  deteriorate  into  the  simpler  oxides,  namely,  iron, 
silica,  and  aluminum  oxides.  The  result  may  be  a  denser  structure 
and  a  loss  of  base-adsorbing  capacity.  Perhaps  a  similar  condition 
may  come  about  with  a  soil  impoverished  of  replaceable  calcium  in 
the  case  of  a  sodium-saturated,  adsorbing  complex  with  a  "black 
alkali"  condition,  which  may  be  a  possible  cause  of  "slick  spots."  It 
is  conceivable  that  heavy  and  continued  applications  of  sulfur  may 
hasten  removal  of  calcium  ion  and  ultimately  lead  to  soil  deterioration, 
especially  under  conditions  favorable  for  leaching.  After  an  initial 
application,  subsequent  sulfur  treatments  are  often  effective  if  applied 
at  a  lighter  rate.  Where  fertilized  alfalfa  is  consumed  on  the  farm 
and  over-irrigation  is  avoided,  the  increase  in  organic  matter  caused 
by  moderate  applications  (that  is,  80  to  100  pounds  an  acre)  of  sulfur 
every  3  or  4  years  may  have  little  effect  on  soil  deterioration.  It 
would  seem  that  the  use  of  sulfur  as  a  fertilizer  may  be  more  safely 
practiced  on  basaltic  soils  that  are  liberally  supplied  with  different 
forms  of  calcium. 

Does  Sulfur  Improve  Reaction  of  Arid  Soils  for  Alfalfa? 

Nitrate  is  known  to  be  taken  into  the  plant  better  under  slightly 
acid  conditions,  and  sulfur  may  improve  reaction  for  nitrate  adsorp- 
tion by  alfalfa.  Johnston  seems  to  find31  that  sulfate  is  taken  up 
by  alfalfa  best  when  the  pH  value  of  the  culture  medium  is  about  5.8. 
Iron  and  phosphate  are  known  to  be  relatively  insoluble  under  alkaline 
conditions.  Sulfur  tends  to  increase  the  solubility  of  these  nutrients 
up  to  a  point  where  the  calcium  dissolved  begins  to  react  and  cause 
reprecipitation.  Sulfur  doubled  the  amount  of  iron  in  solution  in 
Antelope  clay  adobe.  Ferric  chloride  applied  by  spraying  on  young 
growth  on  this  soil  resulted  in  the  same  improvement  in  color  and 
yield  that  has  been  characteristic  of  sulfur-treated  plats. 

In  nutrient  solutions  correction  of  reaction  by  addition  of  dilute 
sulfuric  acid  secured  larger  growth  and  better  color  of  alfalfa  than 
resulted  from  addition  of  hydrochloric  acid.     This  sulfate  may  have 


1927]  Powers:  Studies  of  Sulfur  in  B elation  to  the  Soil  Solution  165 

affected  the  form  of  iron  in  the  culture  solution  or  it  may  have  acted 
directly.  Possibly  the  chlorine  in  the  small  amount  added  was  in- 
jurious. Alfalfa  grows  best  in  a  slightly  acid  medium,  as  indicated 
by  Theron07  and  confirmed  herein.  The  best  reaction  for  the  alfalfa- 
radicicola  combination  was  found  to  be  about  pH  6.0. 

Sulfur  has  been  found  effective  in  improving  the  reaction  and 
structure  of  alkali  soil  at  Kearney  Park  Experiment  Field,  Califor- 
nia, and  at  Vale  Experiment  Field  in  Eastern  Oregon.30  Sulfur 
application  may  result  in  improved  permeability  in  alkali  land,  and, 
by  improvement  in  soil  structure  or  possibly  by  modification  of  surface 
tension,  may  render  soil  more  drought-resistant. 

There  are  numerous  other  effects  of  sulfur  on  physical,  chemical, 
and  biological  conditions  related  to  plant  nutrition.  The  three  factors 
discussed  above  have  stood  out  as  being  of  chief  importance  in  these 
studies  with  the  soil  solution.  Which  of  these  effects  will  be  of  major 
importance  may  depend  on  the  particular  soil  and  conditions  at  hand. 


SUMMARY 

1.  Sulfur  and  sulfates  applied  to  Madera  sand  soil  in  pot  tests 
caused  marked  increase  in  calcium  ion  and  a  definite  increase  in  other 
bases  in  the  displaced  soil  solution.  Calcium  and  sulfate  ions  go  into 
the  alfalfa  plant  especially  well  together. 

2.  Heavy  applications  of  sulfur  resulted  in  increased  soil  acidity, 
which  caused  an  increase  in  phosphate  and  iron  content  of  the  soil 
solution  up  to  a  certain  point,  after  which  bases  dissolved  or  replaced 
tended  to  precipitate  these  two  ions  from  the  soil  solution. 

3.  Heavy  application  of  sulfur  tended  to  inhibit  nitrification, 
though  the  normal  application,  or  100  pounds  per  acre,  on  arid  soils 
may  increase  growth  and  nitrogen  in  the  soil. 

4.  Evidence  was  found  of  base  exchange  as  sulfur  oxidation  in- 
creased the  concentration  of  hydrogen  ion  and  then  of  other  cations. 
Fixation  and  exchange  of  bases  applied  in  sulfates,  as  in  potassium 
sulfate,  was  noted. 

5.  Analyses  of  displaced  soil  solutions  of  several  sulfured  and 
unsulfured  soils  from  fertilizer  experiment  fields  tend  to  confirm 
results  secured  with  Madera  sand  and  further  indicate  that  the 
sulfate  content  of  some  soils  at  certain  seasons  is  very  low.  Further, 
that  the  effect  of  sulfur  will  depend  much  upon  the  particular  soil 
at  hand. 


166  University  of  California  Publications  in  Agricultural  Sciences^       [Vol.5 

6.  Sulfur  is  needed  most  by  alfalfa  during  the  early  weeks  of  the 
growth  period.  Sulfur  applications  increase  sulfofication  and  the 
sulfate  content  of  the  soil  solution,  and  they  may  in  turn  serve  to 
bring  bases  into  solution,  resulting  in  a  more  concentrated  soil  solution 
and  decreased  transpiration. 

7.  Water  culture  experiments  indicate  that  a  concentration  of  48 
to  24  parts  per  million  of  sulfate  is  most  favorable  for  the  growth  of 
alfalfa  under  the  conditions  of  the  trial.  The  maximum  production 
secured  per  milligram  of  sulfur  was  .18  gm.  alfalfa  and  was  produced 
with  a  solution  having  an  initial  sulfate  content  of  15  parts  per 
million. 

8.  An  average  application  of  sulfur  appears  to  improve  the  reaction 
of  arid  soils  for  alfalfa  nutrition,  resulting  in  increased  growth  and 
higher  chlorophyll  and  sulfate  content. 

9.  It  is  concluded  (a)  that  some  soils  may  have  a  sulfate  content 
which  is  unfavorably  low  for  best  growth  of  alfalfa,  especially  early 
in  the  growth  period;  (b)  that  sulfur  oxidizes  to  sulfate  and  brings 
additional  calcium  and  other  bases  into  solution;  (c)  that  sulfur  in 
moderate  amounts  improves  the  reaction  of  arid  soils  for  alfalfa 
nutrition;  (d)  that  the  sulfur  applications  which  are  of  greatest 
benefit  will  depend  on  the  soil  at  hand;  and  (e)  that  ordinary  appli- 
cations of  sulfur  for  alfalfa  on  the  arid  basaltic  soils  or  soils  liberally 
supplied  with  calcium  compounds  is  probably  good  practice,  especially 
where  the  growth  secured  is  consumed  on  the  farm. 


19271  Powers:  Studies  of  Svlfur  in  Bclation  to  the  Soil  Solution  167 


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